JDK下sun.net.www.protocol.http.HttpURLConnection类-----Http客户端实现类的实现分析

HttpClient类是进行TCP连接的实现类，

package sun.net.www.http;

import java.io.*;
import java.net.*;
import java.util.*;
import sun.net.NetworkClient;
import sun.net.ProgressSource;
import sun.net.ProgressMonitor;
import sun.net.www.MessageHeader;
import sun.net.www.HeaderParser;
import sun.net.www.MeteredStream;
import sun.net.www.ParseUtil;
import sun.net.www.protocol.http.HttpURLConnection;
import sun.misc.RegexpPool;

import java.security.*;
/**
 * @author Herb Jellinek
 * @author Dave Brown
 */
public class HttpClient extends NetworkClient {
    // whether this httpclient comes from the cache
    protected boolean cachedHttpClient = false;

    private boolean inCache;

    protected CookieHandler cookieHandler;

    // Http requests we send
    MessageHeader requests;

    // Http data we send with the headers
    PosterOutputStream poster = null;

    // if we've had one io error
    boolean failedOnce = false;

    /** regexp pool of hosts for which we should connect directly, not Proxy
     *  these are intialized from a property.
     */
    private static RegexpPool nonProxyHostsPool = null;

    /** The string source of nonProxyHostsPool
     */
    private static String nonProxyHostsSource = null;

    /** Response code for CONTINUE */
    private static final int    HTTP_CONTINUE = 100;

    /** Default port number for http daemons. REMIND: make these private */
    static final int    httpPortNumber = 80;

    /** return default port number (subclasses may override) */
    protected int getDefaultPort () { return httpPortNumber; }

    static private int getDefaultPort(String proto) {
        if ("http".equalsIgnoreCase(proto))
            return 80;
        if ("https".equalsIgnoreCase(proto))
            return 443;
        return -1;
    }

    /* The following three data members are left in for binary */
    /* backwards-compatibility.  Unfortunately, HotJava sets them directly */
    /* when it wants to change the settings.  The new design has us not */
    /* cache these, so this is unnecessary, but eliminating the data members */
    /* would break HJB 1.1 under JDK 1.2. */
    /* */
    /* These data members are not used, and their values are meaningless. */
    /* REMIND:  Take them out for JDK 2.0! */
    /**
     * @deprecated
     */
    //    public static String proxyHost = null;
    /**
     * @deprecated
     */
    //    public static int proxyPort = 80;

    /* instance-specific proxy fields override the static fields if set.
     * Used by FTP.  These are set to the true proxy host/port if
     * usingProxy is true.
     */
    //    private String instProxy = null;
    //    private int instProxyPort = -1;

    /* All proxying (generic as well as instance-specific) may be
     * disabled through use of this flag
     */
    protected boolean proxyDisabled;

    // are we using proxy in this instance?
    public boolean usingProxy = false;
    // target host, port for the URL
    protected String host;
    protected int port;

    /* where we cache currently open, persistent connections */
    protected static KeepAliveCache kac = new KeepAliveCache();

    private static boolean keepAliveProp = true;

    // retryPostProp is true by default so as to preserve behavior
    // from previous releases.
    private static boolean retryPostProp = true;

    volatile boolean keepingAlive = false;     /* this is a keep-alive connection */
    int keepAliveConnections = -1;    /* number of keep-alives left */

    /**Idle timeout value, in milliseconds. Zero means infinity,
     * iff keepingAlive=true.
     * Unfortunately, we can't always believe this one.  If I'm connected
     * through a Netscape proxy to a server that sent me a keep-alive
     * time of 15 sec, the proxy unilaterally terminates my connection
     * after 5 sec.  So we have to hard code our effective timeout to
     * 4 sec for the case where we're using a proxy. *SIGH*
     */
    int keepAliveTimeout = 0;

    /** whether the response is to be cached */
    private CacheRequest cacheRequest = null;

    /** Url being fetched. */
    protected URL       url;

    /* if set, the client will be reused and must not be put in cache */
    public boolean reuse = false;

    /**
     * A NOP method kept for backwards binary compatibility
     * @deprecated -- system properties are no longer cached.
     */
    @Deprecated
    public static synchronized void resetProperties() {
    }

    int getKeepAliveTimeout() {
        return keepAliveTimeout;
    }

    static {
        String keepAlive = java.security.AccessController.doPrivileged(
            new sun.security.action.GetPropertyAction("http.keepAlive"));

        String retryPost = java.security.AccessController.doPrivileged(
            new sun.security.action.GetPropertyAction("sun.net.http.retryPost"));

        if (keepAlive != null) {
            keepAliveProp = Boolean.valueOf(keepAlive).booleanValue();
        } else {
            keepAliveProp = true;
        }

        if (retryPost != null) {
            retryPostProp = Boolean.valueOf(retryPost).booleanValue();
        } else
            retryPostProp = true;

    }

    /**
     * @return true iff http keep alive is set (i.e. enabled).  Defaults
     *          to true if the system property http.keepAlive isn't set.
     */
    public boolean getHttpKeepAliveSet() {
        return keepAliveProp;
    }

    protected HttpClient() {
    }

    private HttpClient(URL url)
    throws IOException {
        this(url, (String)null, -1, false);
    }

    protected HttpClient(URL url,
                         boolean proxyDisabled) throws IOException {
        this(url, null, -1, proxyDisabled);
    }

    /* This package-only CTOR should only be used for FTP piggy-backed on HTTP
     * HTTP URL's that use this won't take advantage of keep-alive.
     * Additionally, this constructor may be used as a last resort when the
     * first HttpClient gotten through New() failed (probably b/c of a
     * Keep-Alive mismatch).
     *
     * XXX That documentation is wrong ... it's not package-private any more
     */
    public HttpClient(URL url, String proxyHost, int proxyPort)
    throws IOException {
        this(url, proxyHost, proxyPort, false);
    }
    //该构造方法的最后一行openserver()方法进行了TCP连接
    protected HttpClient(URL url, Proxy p, int to) throws IOException {
        proxy = (p == null) ? Proxy.NO_PROXY : p;
        this.host = url.getHost();
        this.url = url;
        port = url.getPort();
        if (port == -1) {
            port = getDefaultPort();
        }
        setConnectTimeout(to);

        // get the cookieHandler if there is any
        cookieHandler = (CookieHandler)java.security.AccessController.doPrivileged(
            new java.security.PrivilegedAction() {
                public Object run() {
                    return CookieHandler.getDefault();
                }
            });

        openServer();
    }

    static protected Proxy newHttpProxy(String proxyHost, int proxyPort,
                                      String proto) {
        if (proxyHost == null || proto == null)
            return Proxy.NO_PROXY;
        int pport = proxyPort < 0 ? getDefaultPort(proto) : proxyPort;
        InetSocketAddress saddr = InetSocketAddress.createUnresolved(proxyHost, pport);
        return new Proxy(Proxy.Type.HTTP, saddr);
    }

    /*
     * This constructor gives "ultimate" flexibility, including the ability
     * to bypass implicit proxying.  Sometimes we need to be using tunneling
     * (transport or network level) instead of proxying (application level),
     * for example when we don't want the application level data to become
     * visible to third parties.
     *
     * @param url               the URL to which we're connecting
     * @param proxy             proxy to use for this URL (e.g. forwarding)
     * @param proxyPort         proxy port to use for this URL
     * @param proxyDisabled     true to disable default proxying
     */
    private HttpClient(URL url, String proxyHost, int proxyPort,
                       boolean proxyDisabled)
        throws IOException {
        this(url, proxyDisabled ? Proxy.NO_PROXY :
             newHttpProxy(proxyHost, proxyPort, "http"), -1);
    }

    public HttpClient(URL url, String proxyHost, int proxyPort,
                       boolean proxyDisabled, int to)
        throws IOException {
        this(url, proxyDisabled ? Proxy.NO_PROXY :
             newHttpProxy(proxyHost, proxyPort, "http"), to);
    }

    /* This class has no public constructor for HTTP.  This method is used to
     * get an HttpClient to the specifed URL.  If there's currently an
     * active HttpClient to that server/port, you'll get that one.
     */
    public static HttpClient New(URL url)
    throws IOException {
        return HttpClient.New(url, Proxy.NO_PROXY, -1, true);
    }

    public static HttpClient New(URL url, boolean useCache)
        throws IOException {
        return HttpClient.New(url, Proxy.NO_PROXY, -1, useCache);
    }

    public static HttpClient New(URL url, Proxy p, int to, boolean useCache)
        throws IOException {
        if (p == null) {
            p = Proxy.NO_PROXY;
        }
        HttpClient ret = null;
        /* see if one's already around */
        if (useCache) {
            ret = (HttpClient) kac.get(url, null);
            if (ret != null) {
                if ((ret.proxy != null && ret.proxy.equals(p)) ||
                    (ret.proxy == null && p == null)) {
                    synchronized (ret) {
                        ret.cachedHttpClient = true;
                        assert ret.inCache;
                        ret.inCache = false;
                    }
                } else {
                    // We cannot return this connection to the cache as it's
                    // KeepAliveTimeout will get reset. We simply close the connection.
                    // This should be fine as it is very rare that a connection
                    // to the same host will not use the same proxy.
                    ret.inCache = false;
                    ret.closeServer();
                    ret = null;
                }
            }
        }
        if (ret == null) {
            ret = new HttpClient(url, p, to);
        } else {
            SecurityManager security = System.getSecurityManager();
            if (security != null) {
                if (ret.proxy == Proxy.NO_PROXY || ret.proxy == null) {
                    security.checkConnect(InetAddress.getByName(url.getHost()).getHostAddress(),
                         url.getPort());
                } else {
                    security.checkConnect(url.getHost(), url.getPort());
                }
            }
            ret.url = url;
        }
        return ret;
    }

    public static HttpClient New(URL url, Proxy p, int to) throws IOException {
        return New(url, p, to, true);
    }

    public static HttpClient New(URL url, String proxyHost, int proxyPort,
                                 boolean useCache)
        throws IOException {
        return New(url, newHttpProxy(proxyHost, proxyPort, "http"), -1, useCache);
    }

    public static HttpClient New(URL url, String proxyHost, int proxyPort,
                                 boolean useCache, int to)
        throws IOException {
        return New(url, newHttpProxy(proxyHost, proxyPort, "http"), to, useCache);
    }

    /* return it to the cache as still usable, if:
     * 1) It's keeping alive, AND
     * 2) It still has some connections left, AND
     * 3) It hasn't had a error (PrintStream.checkError())
     * 4) It hasn't timed out
     *
     * If this client is not keepingAlive, it should have been
     * removed from the cache in the parseHeaders() method.
     */

    public void finished() {
        if (reuse) /* will be reused */
            return;
        keepAliveConnections--;
        poster = null;
        if (keepAliveConnections > 0 && isKeepingAlive() &&
               !(serverOutput.checkError())) {
            /* This connection is keepingAlive && still valid.
             * Return it to the cache.
             */
            putInKeepAliveCache();
        } else {
            closeServer();
        }
    }

    protected synchronized void putInKeepAliveCache() {
        if (inCache) {
            assert false : "Duplicate put to keep alive cache";
            return;
        }
        inCache = true;
        kac.put(url, null, this);
    }

    protected boolean isInKeepAliveCache() {
        return inCache;
    }

    /*
     * Close an idle connection to this URL (if it exists in the
     * cache).
     */
    public void closeIdleConnection() {
        HttpClient http = (HttpClient) kac.get(url, null);
        if (http != null) {
            http.closeServer();
        }
    }

    /* We're very particular here about what our InputStream to the server
     * looks like for reasons that are apparent if you can decipher the
     * method parseHTTP().  That's why this method is overidden from the
     * superclass.
     * server ： 要连接的IP port：要连接的端口
     */
    public void openServer(String server, int port) throws IOException {
        //serverSocket对象是一个Socket对象，是建立连接之后返回的Socket对象，调用父类NetworkClient类的doConnect方法
        serverSocket = doConnect(server, port);
        try {
            serverOutput = new PrintStream(
                new BufferedOutputStream(serverSocket.getOutputStream()),
                                         false, encoding);
        } catch (UnsupportedEncodingException e) {
            throw new InternalError(encoding+" encoding not found");
        }
        serverSocket.setTcpNoDelay(true);
    }

    /*
     * Returns true if the http request should be tunneled through proxy.
     * An example where this is the case is Https.
     */
    public boolean needsTunneling() {
        return false;
    }

    /*
     * Returns true if this httpclient is from cache
     */
    public boolean isCachedConnection() {
        return cachedHttpClient;
    }

    /*
     * Finish any work left after the socket connection is
     * established.  In the normal http case, it's a NO-OP. Subclass
     * may need to override this. An example is Https, where for
     * direct connection to the origin server, ssl handshake needs to
     * be done; for proxy tunneling, the socket needs to be converted
     * into an SSL socket before ssl handshake can take place.
     */
    public void afterConnect() throws IOException, UnknownHostException {
        // NO-OP. Needs to be overwritten by HttpsClient
    }

    /*
     * call openServer in a privileged block
     */
    private synchronized void privilegedOpenServer(final InetSocketAddress server)
         throws IOException
    {
        try {
            java.security.AccessController.doPrivileged(
                new java.security.PrivilegedExceptionAction() {
                public Object run() throws IOException {
                    openServer(server.getHostName(), server.getPort());
                    return null;
                }
            });
        } catch (java.security.PrivilegedActionException pae) {
            throw (IOException) pae.getException();
        }
    }

    /*
     * call super.openServer
     */
    private void superOpenServer(final String proxyHost,
                                 final int proxyPort)
        throws IOException, UnknownHostException
    {
        super.openServer(proxyHost, proxyPort);
    }

    /*
     * call super.openServer in a privileged block
     */
    private synchronized void privilegedSuperOpenServer(final String proxyHost,
                                                        final int proxyPort)
        throws IOException
    {
        try {
            java.security.AccessController.doPrivileged(
                new java.security.PrivilegedExceptionAction() {
                public Object run() throws IOException
                {
                    superOpenServer(proxyHost, proxyPort);
                    return null;
                }
            });
        } catch (java.security.PrivilegedActionException pae) {
            throw (IOException) pae.getException();
        }
    }

    /*
     *无参数的openServer方法，实现开启TCP连接工作
     */
    protected synchronized void openServer() throws IOException {

        SecurityManager security = System.getSecurityManager();

        if (keepingAlive) { // already opened
            if (security != null) {
                security.checkConnect(host, port);
            }

            return;
        }

        String urlHost = url.getHost().toLowerCase();

        if (url.getProtocol().equals("http") ||
            url.getProtocol().equals("https") ) {

            if ((proxy != null) && (proxy.type() == Proxy.Type.HTTP)) {
                sun.net.www.URLConnection.setProxiedHost(host);
                if (security != null) {
                    security.checkConnect(host, port);
                }
                privilegedOpenServer((InetSocketAddress) proxy.address());
                usingProxy = true;
                return;
            } else {
                // make direct connection
                if (security != null) {
                    // redundant?
                    security.checkConnect(host, port);
                }
　　　　　　　　　//调用有参构造方法，传入要连接的host和port
                openServer(host, port);
                usingProxy = false;
                return;
            }

        } else {
            /* we're opening some other kind of url, most likely an
             * ftp url.
             */
            if ((proxy != null) && (proxy.type() == Proxy.Type.HTTP)) {
                sun.net.www.URLConnection.setProxiedHost(host);
                if (security != null) {
                    security.checkConnect(host, port);
                }
                privilegedOpenServer((InetSocketAddress) proxy.address());
                usingProxy = true;
                return;
            } else {
                // make direct connection
                if (security != null) {
                    // redundant?
                    security.checkConnect(host, port);
                }
                super.openServer(host, port);
                usingProxy = false;
                return;
            }
        }
    }

    public String getURLFile() throws IOException {

        String fileName = url.getFile();
        if ((fileName == null) || (fileName.length() == 0))
            fileName = "/";

        /**
         * proxyDisabled is set by subclass HttpsClient!
         */
        if (usingProxy && !proxyDisabled) {
            // Do not use URLStreamHandler.toExternalForm as the fragment
            // should not be part of the RequestURI. It should be an
            // absolute URI which does not have a fragment part.
            StringBuffer result = new StringBuffer(128);
            result.append(url.getProtocol());
            result.append(":");
            if (url.getAuthority() != null && url.getAuthority().length() > 0) {
                result.append("//");
                result.append(url.getAuthority());
            }
            if (url.getPath() != null) {
                result.append(url.getPath());
            }
            if (url.getQuery() != null) {
                result.append('?');
                result.append(url.getQuery());
            }

            fileName =  result.toString();
        }
        if (fileName.indexOf('\n') == -1)
            return fileName;
        else
            throw new java.net.MalformedURLException("Illegal character in URL");
    }

    /**
     * @deprecated
     */
    @Deprecated
    public void writeRequests(MessageHeader head) {
        requests = head;
        requests.print(serverOutput);
        serverOutput.flush();
    }

    public void writeRequests(MessageHeader head,
                              PosterOutputStream pos) throws IOException {
        requests = head;
        requests.print(serverOutput);
        poster = pos;
        if (poster != null)
            poster.writeTo(serverOutput);
        serverOutput.flush();
    }

    /** Parse the first line of the HTTP request.  It usually looks
        something like: "HTTP/1.0 <number> comment\r\n". */

    public boolean parseHTTP(MessageHeader responses, ProgressSource pi, HttpURLConnection httpuc)
    throws IOException {
        /* If "HTTP/*" is found in the beginning, return true.  Let
         * HttpURLConnection parse the mime header itself.
         *
         * If this isn't valid HTTP, then we don't try to parse a header
         * out of the beginning of the response into the responses,
         * and instead just queue up the output stream to it's very beginning.
         * This seems most reasonable, and is what the NN browser does.
         */

        try {
            serverInput = serverSocket.getInputStream();
            serverInput = new BufferedInputStream(serverInput);
            return (parseHTTPHeader(responses, pi, httpuc));
        } catch (SocketTimeoutException stex) {
            // We don't want to retry the request when the app. sets a timeout
            closeServer();
            throw stex;
        } catch (IOException e) {
            closeServer();
            cachedHttpClient = false;
            if (!failedOnce && requests != null) {
                if (httpuc.getRequestMethod().equals("POST") && !retryPostProp) {
                    // do not retry the request
                }  else {
                    // try once more
                    failedOnce = true;
                    openServer();
                    if (needsTunneling()) {
                        httpuc.doTunneling();
                    }
                    afterConnect();
                    writeRequests(requests, poster);
                    return parseHTTP(responses, pi, httpuc);
                }
            }
            throw e;
        }

    }

    public int setTimeout (int timeout) throws SocketException {
        int old = serverSocket.getSoTimeout ();
        serverSocket.setSoTimeout (timeout);
        return old;
    }

    private boolean parseHTTPHeader(MessageHeader responses, ProgressSource pi, HttpURLConnection httpuc)
    throws IOException {
        /* If "HTTP/*" is found in the beginning, return true.  Let
         * HttpURLConnection parse the mime header itself.
         *
         * If this isn't valid HTTP, then we don't try to parse a header
         * out of the beginning of the response into the responses,
         * and instead just queue up the output stream to it's very beginning.
         * This seems most reasonable, and is what the NN browser does.
         */

        keepAliveConnections = -1;
        keepAliveTimeout = 0;

        boolean ret = false;
        byte[] b = new byte[8];

        try {
            int nread = 0;
            serverInput.mark(10);
            while (nread < 8) {
                int r = serverInput.read(b, nread, 8 - nread);
                if (r < 0) {
                    break;
                }
                nread += r;
            }
            String keep=null;
            ret = b[0] == 'H' && b[1] == 'T'
                    && b[2] == 'T' && b[3] == 'P' && b[4] == '/' &&
                b[5] == '1' && b[6] == '.';
            serverInput.reset();
            if (ret) { // is valid HTTP - response started w/ "HTTP/1."
                responses.parseHeader(serverInput);

                // we've finished parsing http headers
                // check if there are any applicable cookies to set (in cache)
                if (cookieHandler != null) {
                    URI uri = ParseUtil.toURI(url);
                    // NOTE: That cast from Map shouldn't be necessary but
                    // a bug in javac is triggered under certain circumstances
                    // So we do put the cast in as a workaround until
                    // it is resolved.
                    if (uri != null)
                        cookieHandler.put(uri, (Map<java.lang.String,java.util.List<java.lang.String>>)responses.getHeaders());
                }

                /* decide if we're keeping alive:
                 * This is a bit tricky.  There's a spec, but most current
                 * servers (10/1/96) that support this differ in dialects.
                 * If the server/client misunderstand each other, the
                 * protocol should fall back onto HTTP/1.0, no keep-alive.
                 */
                if (usingProxy) { // not likely a proxy will return this
                    keep = responses.findValue("Proxy-Connection");
                }
                if (keep == null) {
                    keep = responses.findValue("Connection");
                }
                if (keep != null && keep.toLowerCase().equals("keep-alive")) {
                    /* some servers, notably Apache1.1, send something like:
                     * "Keep-Alive: timeout=15, max=1" which we should respect.
                     */
                    HeaderParser p = new HeaderParser(
                            responses.findValue("Keep-Alive"));
                    if (p != null) {
                        /* default should be larger in case of proxy */
                        keepAliveConnections = p.findInt("max", usingProxy?50:5);
                        keepAliveTimeout = p.findInt("timeout", usingProxy?60:5);
                    }
                } else if (b[7] != '0') {
                    /*
                     * We're talking 1.1 or later. Keep persistent until
                     * the server says to close.
                     */
                    if (keep != null) {
                        /*
                         * The only Connection token we understand is close.
                         * Paranoia: if there is any Connection header then
                         * treat as non-persistent.
                         */
                        keepAliveConnections = 1;
                    } else {
                        keepAliveConnections = 5;
                    }
                }
            } else if (nread != 8) {
                if (!failedOnce && requests != null) {
                    if (httpuc.getRequestMethod().equals("POST") && !retryPostProp) {
                        // do not retry the request
                    } else {
                        failedOnce = true;
                        closeServer();
                        cachedHttpClient = false;
                        openServer();
                        if (needsTunneling()) {
                            httpuc.doTunneling();
                        }
                        afterConnect();
                        writeRequests(requests, poster);
                        return parseHTTP(responses, pi, httpuc);
                    }
                }
                throw new SocketException("Unexpected end of file from server");
            } else {
                // we can't vouche for what this is....
                responses.set("Content-type", "unknown/unknown");
            }
        } catch (IOException e) {
            throw e;
        }

        int code = -1;
        try {
            String resp;
            resp = responses.getValue(0);
            /* should have no leading/trailing LWS
             * expedite the typical case by assuming it has
             * form "HTTP/1.x <WS> 2XX <mumble>"
             */
            int ind;
            ind = resp.indexOf(' ');
            while(resp.charAt(ind) == ' ')
                ind++;
            code = Integer.parseInt(resp.substring(ind, ind + 3));
        } catch (Exception e) {}

        if (code == HTTP_CONTINUE) {
            responses.reset();
            return parseHTTPHeader(responses, pi, httpuc);
        }

        int cl = -1;

        /*
         * Set things up to parse the entity body of the reply.
         * We should be smarter about avoid pointless work when
         * the HTTP method and response code indicate there will be
         * no entity body to parse.
         */
        String te = null;
        try {
            te = responses.findValue("Transfer-Encoding");
        } catch (Exception e) {}
        if (te != null && te.equalsIgnoreCase("chunked")) {
            serverInput = new ChunkedInputStream(serverInput, this, responses);

            /*
             * If keep alive not specified then close after the stream
             * has completed.
             */
            if (keepAliveConnections <= 1) {
                keepAliveConnections = 1;
                keepingAlive = false;
            } else {
                keepingAlive = true;
            }
            failedOnce = false;
        } else {

            /*
             * If it's a keep alive connection then we will keep
             * (alive if :-
             * 1. content-length is specified, or
             * 2. "Not-Modified" or "No-Content" responses - RFC 2616 states that
             *    204 or 304 response must not include a message body.
             */
            try {
                cl = Integer.parseInt(responses.findValue("content-length"));
            } catch (Exception e) {}

            String requestLine = requests.getKey(0);

            if ((requestLine != null &&
                 (requestLine.startsWith("HEAD"))) ||
                code == HttpURLConnection.HTTP_NOT_MODIFIED ||
                code == HttpURLConnection.HTTP_NO_CONTENT) {
                cl = 0;
            }

            if (keepAliveConnections > 1 &&
                (cl >= 0 ||
                 code == HttpURLConnection.HTTP_NOT_MODIFIED ||
                 code == HttpURLConnection.HTTP_NO_CONTENT)) {
                keepingAlive = true;
                failedOnce = false;
            } else if (keepingAlive) {
                /* Previously we were keeping alive, and now we're not.  Remove
                 * this from the cache (but only here, once) - otherwise we get
                 * multiple removes and the cache count gets messed up.
                 */
                keepingAlive=false;
            }
        }

        /* wrap a KeepAliveStream/MeteredStream around it if appropriate */

        if (cl > 0) {
            // In this case, content length is well known, so it is okay
            // to wrap the input stream with KeepAliveStream/MeteredStream.

            if (pi != null) {
                // Progress monitor is enabled
                pi.setContentType(responses.findValue("content-type"));
            }

            if (isKeepingAlive())   {
                // Wrap KeepAliveStream if keep alive is enabled.
                serverInput = new KeepAliveStream(serverInput, pi, cl, this);
                failedOnce = false;
            }
            else        {
                serverInput = new MeteredStream(serverInput, pi, cl);
            }
        }
        else if (cl == -1)  {
            // In this case, content length is unknown - the input
            // stream would simply be a regular InputStream or
            // ChunkedInputStream.

            if (pi != null) {
                // Progress monitoring is enabled.

                pi.setContentType(responses.findValue("content-type"));

                // Wrap MeteredStream for tracking indeterministic
                // progress, even if the input stream is ChunkedInputStream.
                serverInput = new MeteredStream(serverInput, pi, cl);
            }
            else    {
                // Progress monitoring is disabled, and there is no
                // need to wrap an unknown length input stream.

                // ** This is an no-op **
            }
        }
        else    {
            if (pi != null)
                pi.finishTracking();
        }

        return ret;
    }

    public synchronized InputStream getInputStream() {
        return serverInput;
    }

    public OutputStream getOutputStream() {
        return serverOutput;
    }

    public String toString() {
        return getClass().getName()+"("+url+")";
    }

    public final boolean isKeepingAlive() {
        return getHttpKeepAliveSet() && keepingAlive;
    }

    public void setCacheRequest(CacheRequest cacheRequest) {
        this.cacheRequest = cacheRequest;
    }

    CacheRequest getCacheRequest() {
        return cacheRequest;
    }

    protected void finalize() throws Throwable {
        // This should do nothing.  The stream finalizer will
        // close the fd.
    }

    public void setDoNotRetry(boolean value) {
        // failedOnce is used to determine if a request should be retried.
        failedOnce = value;
    }

    /* Use only on connections in error. */
    public void closeServer() {
        try {
            keepingAlive = false;
            serverSocket.close();
        } catch (Exception e) {}
    }

    /**
     * @return the proxy host being used for this client, or null
     *          if we're not going through a proxy
     */
    public String getProxyHostUsed() {
        if (!usingProxy) {
            return null;
        } else {
            return ((InetSocketAddress)proxy.address()).getHostName();
        }
    }

    /**
     * @return the proxy port being used for this client.  Meaningless
     *          if getProxyHostUsed() gives null.
     */
    public int getProxyPortUsed() {
        if (usingProxy)
            return ((InetSocketAddress)proxy.address()).getPort();
        return -1;
    }
}

/*
 * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package sun.net;

import java.io.*;
import java.net.Socket;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.UnknownHostException;
import java.net.Proxy;
import java.util.Arrays;
import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * This is the base class for network clients.
 *
 * @author      Jonathan Payne
 */
public class NetworkClient {
    protected Proxy     proxy = Proxy.NO_PROXY;
    /** Socket for communicating with server. */
    protected Socket    serverSocket = null;

    /** Stream for printing to the server. */
    public PrintStream  serverOutput;

    /** Buffered stream for reading replies from server. */
    public InputStream  serverInput;

    protected static int defaultSoTimeout;
    protected static int defaultConnectTimeout;

    protected int readTimeout = -1;
    protected int connectTimeout = -1;
    /* Name of encoding to use for output */
    protected static String encoding;

    static {
        final int vals[] = {0, 0};
        final String encs[] = { null };

        AccessController.doPrivileged(
                new PrivilegedAction() {
                    public Object run() {
                        vals[0] = Integer.getInteger("sun.net.client.defaultReadTimeout", 0).intValue();
                        vals[1] = Integer.getInteger("sun.net.client.defaultConnectTimeout", 0).intValue();
                        encs[0] = System.getProperty("file.encoding", "ISO8859_1");
                        return null;
            }
        });
        if (vals[0] == 0)
            defaultSoTimeout = -1;
        else
            defaultSoTimeout = vals[0];

        if (vals[1] == 0)
            defaultConnectTimeout = -1;
        else
            defaultConnectTimeout = vals[1];

        encoding = encs[0];
        try {
            if (!isASCIISuperset (encoding)) {
                encoding = "ISO8859_1";
            }
        } catch (Exception e) {
            encoding = "ISO8859_1";
        }
    }

    /**
     * Test the named character encoding to verify that it converts ASCII
     * characters correctly. We have to use an ASCII based encoding, or else
     * the NetworkClients will not work correctly in EBCDIC based systems.
     * However, we cannot just use ASCII or ISO8859_1 universally, because in
     * Asian locales, non-ASCII characters may be embedded in otherwise
     * ASCII based protocols (eg. HTTP). The specifications (RFC2616, 2398)
     * are a little ambiguous in this matter. For instance, RFC2398 [part 2.1]
     * says that the HTTP request URI should be escaped using a defined
     * mechanism, but there is no way to specify in the escaped string what
     * the original character set is. It is not correct to assume that
     * UTF-8 is always used (as in URLs in HTML 4.0).  For this reason,
     * until the specifications are updated to deal with this issue more
     * comprehensively, and more importantly, HTTP servers are known to
     * support these mechanisms, we will maintain the current behavior
     * where it is possible to send non-ASCII characters in their original
     * unescaped form.
     */
    private static boolean isASCIISuperset (String encoding) throws Exception {
        String chkS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"+
                        "abcdefghijklmnopqrstuvwxyz-_.!~*'();/?:@&=+$,";

        // Expected byte sequence for string above
        byte[] chkB = { 48,49,50,51,52,53,54,55,56,57,65,66,67,68,69,70,71,72,
                73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,97,98,99,
                100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,
                115,116,117,118,119,120,121,122,45,95,46,33,126,42,39,40,41,59,
                47,63,58,64,38,61,43,36,44};

        byte[] b = chkS.getBytes (encoding);
        return Arrays.equals (b, chkB);
    }

    /** Open a connection to the server. */
    public void openServer(String server, int port)
        throws IOException, UnknownHostException {
        if (serverSocket != null)
            closeServer();
        serverSocket = doConnect (server, port);
        try {
            serverOutput = new PrintStream(new BufferedOutputStream(
                                        serverSocket.getOutputStream()),
                                        true, encoding);
        } catch (UnsupportedEncodingException e) {
            throw new InternalError(encoding +"encoding not found");
        }
        serverInput = new BufferedInputStream(serverSocket.getInputStream());
    }

    /**
     * Return a socket connected to the server, with any
     * appropriate options pre-established
     */
    protected Socket doConnect (String server, int port)
    throws IOException, UnknownHostException {
        Socket s;
        if (proxy != null) {
            if (proxy.type() == Proxy.Type.SOCKS) {
                s = (Socket) AccessController.doPrivileged(
                               new PrivilegedAction() {
                                   public Object run() {
                                       return new Socket(proxy);
                                   }});
            } else if (proxy.type() == Proxy.Type.DIRECT) {
                s = createSocket();
            } else {
                // Still connecting through a proxy
                // server & port will be the proxy address and port
                s = new Socket(Proxy.NO_PROXY);
            }
        } else
            s = createSocket();
        // Instance specific timeouts do have priority, that means
        // connectTimeout & readTimeout (-1 means not set)
        // Then global default timeouts
        // Then no timeout.
        if (connectTimeout >= 0) {
            s.connect(new InetSocketAddress(server, port), connectTimeout);
        } else {
            if (defaultConnectTimeout > 0) {
                s.connect(new InetSocketAddress(server, port), defaultConnectTimeout);
            } else {
                s.connect(new InetSocketAddress(server, port));
            }
        }
        if (readTimeout >= 0)
            s.setSoTimeout(readTimeout);
        else if (defaultSoTimeout > 0) {
            s.setSoTimeout(defaultSoTimeout);
        }
        return s;
    }

    /**
     * The following method, createSocket, is provided to allow the
     * https client to override it so that it may use its socket factory
     * to create the socket.
     */
    protected Socket createSocket() throws IOException {
        return new java.net.Socket();
    }

    protected InetAddress getLocalAddress() throws IOException {
        if (serverSocket == null)
            throw new IOException("not connected");
        return serverSocket.getLocalAddress();
    }

    /** Close an open connection to the server. */
    public void closeServer() throws IOException {
        if (! serverIsOpen()) {
            return;
        }
        serverSocket.close();
        serverSocket = null;
        serverInput = null;
        serverOutput = null;
    }

    /** Return server connection status */
    public boolean serverIsOpen() {
        return serverSocket != null;
    }

    /** Create connection with host <i>host</i> on port <i>port</i> */
    public NetworkClient(String host, int port) throws IOException {
        openServer(host, port);
    }

    public NetworkClient() {}

    public void setConnectTimeout(int timeout) {
        connectTimeout = timeout;
    }

    public int getConnectTimeout() {
        return connectTimeout;
    }

    public void setReadTimeout(int timeout) {
        if (serverSocket != null && timeout >= 0) {
            try {
                serverSocket.setSoTimeout(timeout);
            } catch(IOException e) {
                // We tried...
            }
        }
        readTimeout = timeout;
    }

    public int getReadTimeout() {
        return readTimeout;
    }
}

　

----------------------------------------------------------------------------------------------------------------------------------------------

下面是sun.net.NetworkClient类中的doConnect(String server,int port)方法，具体执行了创建TCP连接的工作

/**

public void openServer(String server, int port) throws IOException {
        serverSocket = doConnect(server, port);
        try {
            serverOutput = new PrintStream(
                new BufferedOutputStream(serverSocket.getOutputStream()),
                                         false, encoding);
        } catch (UnsupportedEncodingException e) {
            throw new InternalError(encoding+" encoding not found");
        }
        serverSocket.setTcpNoDelay(true);
    }

　　

* Return a socket connected to the server, with any appropriate options * pre-established */ protected Socket doConnect(String server, int port) throws IOException, UnknownHostException { Socket s; if (proxy != null) { if (proxy.type() == Proxy.Type.SOCKS) { s = (Socket) AccessController.doPrivileged(new PrivilegedAction() { public Object run() { return new Socket(proxy); } }); } else if (proxy.type() == Proxy.Type.DIRECT) { s = createSocket(); } else { // Still connecting through a proxy // server & port will be the proxy address and port s = new Socket(Proxy.NO_PROXY); } } else s = createSocket(); // Instance specific timeouts do have priority, that means // connectTimeout & readTimeout (-1 means not set) // Then global default timeouts // Then no timeout. if (connectTimeout >= 0) { s.connect(new InetSocketAddress(server, port), connectTimeout); } else { if (defaultConnectTimeout > 0) { s.connect(new InetSocketAddress(server, port), defaultConnectTimeout); } else { s.connect(new InetSocketAddress(server, port)); } } if (readTimeout >= 0) s.setSoTimeout(readTimeout); else if (defaultSoTimeout > 0) { s.setSoTimeout(defaultSoTimeout); } return s; }

(1)final URL url = new URL(str);

final HttpURLConnection conn = (HttpURLConnection)url.openConnection();

.........

.........//对Connection进行一系列的参数设置

final OutputStream outputStream = conn.getOutputStream()

outputStream.write(body.getBytes（“UTF-8”）)；

sun.net.www.protocol.http.HttpURLConnection类当中的getOutputStream()方法

 /*
     * Allowable input/output sequences:
     * [interpreted as POST/PUT]
     * - get output, [write output,] get input, [read input]
     * - get output, [write output]
     * [interpreted as GET]
     * - get input, [read input]
     * Disallowed:
     * - get input, [read input,] get output, [write output]
     */
    public synchronized OutputStream getOutputStream() throws IOException
    {

        try
        {
            if (!doOutput)
            {
                throw new ProtocolException("cannot write to a URLConnection" + " if doOutput=false - call setDoOutput(true)");
            }

            if (method.equals("GET"))
            {
                method = "POST"; // Backward compatibility
            }
            if (!"POST".equals(method) && !"PUT".equals(method) && "http".equals(url.getProtocol()))
            {
                throw new ProtocolException("HTTP method " + method + " doesn't support output");
            }

            // if there's already an input stream open, throw an exception
            if (inputStream != null)
            {
                throw new ProtocolException("Cannot write output after reading input.");
            }

            if (!checkReuseConnection())
                connect();

            /*
             * REMIND: This exists to fix the HttpsURLConnection subclass.
             * Hotjava needs to run on JDK1.1FCS. Do proper fix in subclass for
             * 1.2 and remove this.
             */

            if (streaming() && strOutputStream == null)
            {
                writeRequests();
            }
            ps = (PrintStream) http.getOutputStream();
            if (streaming())
            {
                if (strOutputStream == null)
                {
                    if (fixedContentLength != -1)
                    {
                        strOutputStream = new StreamingOutputStream(ps, fixedContentLength);
                    }
                    else if (chunkLength != -1)
                    {
                        strOutputStream = new StreamingOutputStream(new ChunkedOutputStream(ps, chunkLength), -1);
                    }
                }
                return strOutputStream;
            }
            else
            {
                if (poster == null)
                {
                    poster = new PosterOutputStream();
                }
                return poster;
            }
        }
        catch(RuntimeException e)
        {
            disconnectInternal();
            throw e;
        }
        catch(IOException e)
        {
            disconnectInternal();
            throw e;
        }
    }

(2) 调用本类的connect()方法

// overridden in HTTPS subclass    
public void connect() throws IOException {
        plainConnect();
    }

(3) 继续调用本类的plainConnect()方法

connected变量是java.net.URLConnection类当中的变量

/**
* If <code>false</code>, this connection object has not created a
* communications link to the specified URL. If <code>true</code>,
* the communications link has been established.
*/
protected boolean connected = false;

------

关于Cache，应该是个优化的重点

cacheHandler类是java.net.ResponseCache接口的实现类

protected void plainConnect()  throws IOException {
        if (connected) {
            return;
        }
        // try to see if request can be served from local cache
        if (cacheHandler != null && getUseCaches()) {
            try {
                URI uri = ParseUtil.toURI(url);
                if (uri != null) {
                    cachedResponse = cacheHandler.get(uri, getRequestMethod(), requests.getHeaders(EXCLUDE_HEADERS));
                    if ("https".equalsIgnoreCase(uri.getScheme())
                        && !(cachedResponse instanceof SecureCacheResponse)) {
                        cachedResponse = null;
                    }
                    if (cachedResponse != null) {
                        cachedHeaders = mapToMessageHeader(cachedResponse.getHeaders());
                        cachedInputStream = cachedResponse.getBody();
                    }
                }
            } catch (IOException ioex) {
                // ignore and commence normal connection
            }
            if (cachedHeaders != null && cachedInputStream != null) {
                connected = true;
                return;
            } else {
                cachedResponse = null;
            }
        }
        try {
            /* Try to open connections using the following scheme,
             * return on the first one that's successful:
             * 1) if (instProxy != null)
             *        connect to instProxy; raise exception if failed
             * 2) else use system default ProxySelector
             * 3) is 2) fails, make direct connection
             */

            if (instProxy == null) { // no instance Proxy is set
                /**
                 * Do we have to use a proxy?
                 */
                ProxySelector sel = (ProxySelector)
                    java.security.AccessController.doPrivileged(
                             new java.security.PrivilegedAction() {
                                 public Object run() {
                                     return ProxySelector.getDefault();
                                 }
                             });
                Proxy p = null;
                if (sel != null) {
                    URI uri = sun.net.www.ParseUtil.toURI(url);
                    Iterator<Proxy> it = sel.select(uri).iterator();
                    while (it.hasNext()) {
                        p = it.next();
                        try {
                            if (!failedOnce) {
                                http = getNewHttpClient(url, p, connectTimeout);
                                http.setReadTimeout(readTimeout);
                            } else {
                                // make sure to construct new connection if first
                                // attempt failed
                                http = getNewHttpClient(url, p, connectTimeout, false);
                                http.setReadTimeout(readTimeout);
                            }
                            break;
                        } catch (IOException ioex) {
                            if (p != Proxy.NO_PROXY) {
                                sel.connectFailed(uri, p.address(), ioex);
                                if (!it.hasNext()) {
                                    // fallback to direct connection
                                    http = getNewHttpClient(url, null, connectTimeout, false);
                                    http.setReadTimeout(readTimeout);
                                    break;
                                }
                            } else {
                                throw ioex;
                            }
                            continue;
                        }
                    }
                } else {
                    // No proxy selector, create http client with no proxy
                    if (!failedOnce) {
                        http = getNewHttpClient(url, null, connectTimeout);
                        http.setReadTimeout(readTimeout);
                    } else {
                        // make sure to construct new connection if first
                        // attempt failed
                        http = getNewHttpClient(url, null, connectTimeout, false);
                        http.setReadTimeout(readTimeout);
                    }
                }
            } else {
                if (!failedOnce) {
                    http = getNewHttpClient(url, instProxy, connectTimeout);
                    http.setReadTimeout(readTimeout);
                } else {
                    // make sure to construct new connection if first
                    // attempt failed
                    http = getNewHttpClient(url, instProxy, connectTimeout, false);
                    http.setReadTimeout(readTimeout);
                }
            }

            ps = (PrintStream)http.getOutputStream();
        } catch (IOException e) {
            throw e;
        }
        // constructor to HTTP client calls openserver
        connected = true;
    }

　　

经过各种纠结判断创建了新的HttpClient对象

在HttpClient对象的构造方法当中

protected HttpClient(URL url, Proxy p, int to) throws IOException {
        proxy = (p == null) ? Proxy.NO_PROXY : p;
        this.host = url.getHost();
        this.url = url;
        port = url.getPort();
        if (port == -1) {
            port = getDefaultPort();
        }
        setConnectTimeout(to);

        // get the cookieHandler if there is any
        cookieHandler = (CookieHandler)java.security.AccessController.doPrivileged(
            new java.security.PrivilegedAction() {
                public Object run() {
                    return CookieHandler.getDefault();
                }
            });

        openServer();
    }

出现了openServer()方法,openServer()方法

protected synchronized void openServer() throws IOException {

        SecurityManager security = System.getSecurityManager();

        if (keepingAlive) { // already opened
            if (security != null) {
                security.checkConnect(host, port);
            }

            return;
        }

        String urlHost = url.getHost().toLowerCase();

        if (url.getProtocol().equals("http") ||
            url.getProtocol().equals("https") ) {

            if ((proxy != null) && (proxy.type() == Proxy.Type.HTTP)) {
                sun.net.www.URLConnection.setProxiedHost(host);
                if (security != null) {
                    security.checkConnect(host, port);
                }
                privilegedOpenServer((InetSocketAddress) proxy.address());
                usingProxy = true;
                return;
            } else {
                // make direct connection
                if (security != null) {
                    // redundant?
                    security.checkConnect(host, port);
                }
                openServer(host, port);
                usingProxy = false;
                return;
            }

        } else {
            /* we're opening some other kind of url, most likely an
             * ftp url.
             */
            if ((proxy != null) && (proxy.type() == Proxy.Type.HTTP)) {
                sun.net.www.URLConnection.setProxiedHost(host);
                if (security != null) {
                    security.checkConnect(host, port);
                }
                privilegedOpenServer((InetSocketAddress) proxy.address());
                usingProxy = true;
                return;
            } else {
                // make direct connection
                if (security != null) {
                    // redundant?
                    security.checkConnect(host, port);
                }
                super.openServer(host, port);
                usingProxy = false;
                return;
            }
        }
    }

最终openServer()方法调用了有参数的openServer方法，该方法中调用了doConnect()方法

public void openServer(String server, int port) throws IOException {
        serverSocket = doConnect(server, port);
        try {
            serverOutput = new PrintStream(
                new BufferedOutputStream(serverSocket.getOutputStream()),
                                         false, encoding);
        } catch (UnsupportedEncodingException e) {
            throw new InternalError(encoding+" encoding not found");
        }
        serverSocket.setTcpNoDelay(true);
    }

最终创建了TCP连接。

socket对象获得了getOutputStream输出流被装饰了两次分别称为了有缓存的Buffered 和Print

由于HttpClient类是NetworkClient类的子类，调用的doConnect方法是父类中方法，最终调用的是connect(SocketAddress xxx)方法来建立连接

   /**
     * Return a socket connected to the server, with any
     * appropriate options pre-established
     */
    protected Socket doConnect (String server, int port)
    throws IOException, UnknownHostException {
        Socket s;
        if (proxy != null) {
            if (proxy.type() == Proxy.Type.SOCKS) {
                s = (Socket) AccessController.doPrivileged(
                               new PrivilegedAction() {
                                   public Object run() {
                                       return new Socket(proxy);
                                   }});
            } else if (proxy.type() == Proxy.Type.DIRECT) {
                s = createSocket();
            } else {
                // Still connecting through a proxy
                // server & port will be the proxy address and port
                s = new Socket(Proxy.NO_PROXY);
            }
        } else
            s = createSocket();
        // Instance specific timeouts do have priority, that means
        // connectTimeout & readTimeout (-1 means not set)
        // Then global default timeouts
        // Then no timeout.
        if (connectTimeout >= 0) {
            s.connect(new InetSocketAddress(server, port), connectTimeout);
        } else {
            if (defaultConnectTimeout > 0) {
                s.connect(new InetSocketAddress(server, port), defaultConnectTimeout);
            } else {
                s.connect(new InetSocketAddress(server, port));
            }
        }
        if (readTimeout >= 0)
            s.setSoTimeout(readTimeout);
        else if (defaultSoTimeout > 0) {
            s.setSoTimeout(defaultSoTimeout);
        }
        return s;
    }