how tomcat works 札记(两)----------一个简单的servlet集装箱

app1

(看着眼前这章建议读者,看how tomcat works 札记(一个)----------一个简单的webserver http://blog.csdn.net/dlf123321/article/details/39378157)

回想我们上一章,我们开发了一个最最简单的webserver,它能够使用户訪问server内的静态资源。当然这是远远不够的,在这一节里,我们就试着让server在能对应静态资源的基础上继续支持servlet。

servlet接口

javax.servlet.Servlet接口定义了五个方法,例如以下:

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我们所使用的servlet都是Servlet接口的间接实现类。

每当我们实例化一个servlet的时候,servlet容器都会先唯一的调用一次init()方法进行初始化,然后再调用service()方法来处理用户的需求,最后在销毁servlet前容器会调用destroy()方法。

我们看看,这一节我们要用的測试servlet。

import javax.servlet.*;

import com.jspsmart.upload.Request;

import java.io.IOException;

import java.io.PrintWriter;

public class PrimitiveServlet implements Servlet {

  public void init(ServletConfig config) throws ServletException {

    System.out.println("init");

  }

  public void service(ServletRequest request, ServletResponse response)

    throws ServletException, IOException {

    System.out.println("from service");

    PrintWriter out = response.getWriter();

    out.println("Hello. Roses are red.");

    out.print("Violets are blue.");

 //   out.flush();

  }

  public void destroy() {

    System.out.println("destroy");

  }

  public String getServletInfo() {

    return null;

  }

  public ServletConfig getServletConfig() {

    return null;

  }

}

Servlet定义的5个方法,它都实现了(只是我们这一节要实现的servlet还没有能力自己主动调用init和destroy方法)。

再看看我们的主方法,程序就从这里開始(和上一节的HttpServer区别不是非常大)

package ex02.pyrmont;

import java.net.Socket;

import java.net.ServerSocket;

import java.net.InetAddress;

import java.io.InputStream;

import java.io.OutputStream;

import java.io.IOException;

public class HttpServer1 {

  /** WEB_ROOT is the directory where our HTML and other files reside.

   *  For this package, WEB_ROOT is the "webroot" directory under the working

   *  directory.

   *  The working directory is the location in the file system

   *  from where the java command was invoked.

   */

  // shutdown command

  private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";

  // the shutdown command received

  private boolean shutdown = false;

  public static void main(String[] args) {

    HttpServer1 server = new HttpServer1();

    server.await();

  }

  public void await() {

    ServerSocket serverSocket = null;

    int port = 8080;

    try {

      serverSocket =  new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));

    }

    catch (IOException e) {

      e.printStackTrace();

      System.exit(1);

    }

    // Loop waiting for a request

    while (!shutdown) {

      Socket socket = null;

      InputStream input = null;

      OutputStream output = null;

      try {

        socket = serverSocket.accept();

        input = socket.getInputStream();

        output = socket.getOutputStream();

        // create Request object and parse

        Request request = new Request(input);

        request.parse();

        // create Response object

        Response response = new Response(output);

        response.setRequest(request);  //没有再这里直接处理静态资源

	                               //而是推断究竟请求的事静态资源还是servlet

        // check if this is a request for a servlet or a static resource

        // a request for a servlet begins with "/servlet/"

        if (request.getUri().startsWith("/servlet/")) {

          ServletProcessor1 processor = new ServletProcessor1();

          processor.process(request, response);

        }

        else {

          StaticResourceProcessor processor = new StaticResourceProcessor();

          processor.process(request, response);

        }

        // Close the socket

        socket.close();

        //check if the previous URI is a shutdown command

        shutdown = request.getUri().equals(SHUTDOWN_COMMAND);

      }

      catch (Exception e) {

        e.printStackTrace();

        System.exit(1);

      }

    }

  }

}

大家能够非常清楚地看到,这部分和上一节的不同主要就在response部分,更准确的说就是在这

if (request.getUri().startsWith("/servlet/")) {

          ServletProcessor1 processor = new ServletProcessor1();

          processor.process(request, response);

        }

        else {

          StaticResourceProcessor processor = new StaticResourceProcessor();

          processor.process(request, response);

        }

我们看看,假设请求是以servlet开头的该怎样处理。

package ex02.pyrmont;

import java.net.URL;

import java.net.URLClassLoader;

import java.net.URLStreamHandler;

import java.io.File;

import java.io.IOException;

import javax.servlet.Servlet;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

public class ServletProcessor1 {

  public void process(Request request, Response response) {

    String uri = request.getUri();

    String servletName = uri.substring(uri.lastIndexOf("/") + 1);

    URLClassLoader loader = null;

    try {

      // create a URLClassLoader   //try部分的主要功能就是产生一个URLClassLoader

      URL[] urls = new URL[1];

      URLStreamHandler streamHandler = null;  

      File classPath = new File(Constants.WEB_ROOT);

      //以下的URL构造函数为

      //java.net.URL.URL(String protocol, String host, String file) throws MalformedURLException

      String repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString() ;

      System.out.println(servletName+"*****"+Constants.WEB_ROOT+"   "+repository);

      //以下的URL构造函数为

      //java.net.URL.URL(URL context, String spec, URLStreamHandler handler) throws MalformedURLException

      //至于 URLStreamHandler是什么东西 临时不必理会

      urls[0] = new URL(null, repository, streamHandler);

      loader = new URLClassLoader(urls);

    }

    catch (IOException e) {

      System.out.println(e.toString() );

    }

    Class<?> myClass = null;

    try {

      myClass = loader.loadClass(servletName);   //载入请求的servlet

    }

    catch (ClassNotFoundException e) {

      System.out.println(e.toString());

    }

    Servlet servlet = null;

    try {

      servlet = (Servlet) myClass.newInstance();  //生成实例 并调用service方法

      servlet.service((ServletRequest) request, (ServletResponse) response);

    }

    catch (Exception e) {

      System.out.println(e.toString());

    }

    catch (Throwable e) {

      System.out.println(e.toString());

    }

  }

}

看看还有一部分,假设请求的不是servlet(这一节就是静态资源)该怎样处理

package ex02.pyrmont;

import java.io.IOException;

public class StaticResourceProcessor {

  public void process(Request request, Response response) {

    try {

      response.sendStaticResource();

    }

    catch (IOException e) {

      e.printStackTrace();

    }

  }

}

跟第一节没有什么差别。

我们的request类要实现ServletRequest接口

package ex02.pyrmont;

import java.io.InputStream;

import java.io.IOException;

import java.io.BufferedReader;

import java.io.UnsupportedEncodingException;

import java.util.Enumeration;

import java.util.Locale;

import java.util.Map;

import javax.servlet.AsyncContext;

import javax.servlet.DispatcherType;

import javax.servlet.RequestDispatcher;

import javax.servlet.ServletContext;

import javax.servlet.ServletInputStream;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

public class Request implements ServletRequest {

  private InputStream input;

  private String uri;

  public Request(InputStream input) {

    this.input = input;

  }

  public String getUri() {

    return uri;

  }

  private String parseUri(String requestString) {

    int index1, index2;

    index1 = requestString.indexOf(' ');

    if (index1 != -1) {

      index2 = requestString.indexOf(' ', index1 + 1);

      if (index2 > index1)

        return requestString.substring(index1 + 1, index2);

    }

    return null;

  }

  public void parse() {

    // Read a set of characters from the socket

    StringBuffer request = new StringBuffer(2048);

    int i;

    byte[] buffer = new byte[2048];

    try {

      i = input.read(buffer);

    }

    catch (IOException e) {

      e.printStackTrace();

      i = -1;

    }

    for (int j=0; j<i; j++) {

      request.append((char) buffer[j]);

    }

    System.out.print(request.toString());

    uri = parseUri(request.toString());

  }

  public void removeAttribute(String attribute) {

  }

  public void setAttribute(String key, Object value) {

  }

  public void setCharacterEncoding(String encoding)

    throws UnsupportedEncodingException {

  }

//缺少的方法 用Eclipse自己主动生成就可以 不再赘述

}

相同的response也要实现ServletResponse接口

package ex02.pyrmont;

import java.io.OutputStream;

import java.io.IOException;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.File;

import java.io.PrintWriter;

import java.util.Locale;

import javax.servlet.ServletResponse;

import javax.servlet.ServletOutputStream;

import com.sun.org.apache.bcel.internal.generic.NEW;

public class Response implements ServletResponse {

  private static final int BUFFER_SIZE = 1024;

  Request request;

  OutputStream output;

  PrintWriter writer;

  public Response(OutputStream output) {

    this.output = output;

  }

  public void setRequest(Request request) {

    this.request = request;

  }

  /* This method is used to serve a static page */

  public void sendStaticResource() throws IOException {

    byte[] bytes = new byte[BUFFER_SIZE];

    FileInputStream fis = null;

    try {

      /* request.getUri has been replaced by request.getRequestURI */

    	System.out.println(Constants.WEB_ROOT+" ***** "+ request.getUri());

      File file = new File(Constants.WEB_ROOT, request.getUri());

      fis = new FileInputStream(file);

      /*

         HTTP Response = Status-Line

           *(( general-header | response-header | entity-header ) CRLF)

           CRLF

           [ message-body ]

         Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF

      */

      int ch = fis.read(bytes, 0, BUFFER_SIZE);

      System.out.println("response  **");

      while (ch!=-1) {

        output.write(bytes, 0, ch);

        ch = fis.read(bytes, 0, BUFFER_SIZE);

      }

    }

    catch (FileNotFoundException e) {

      String errorMessage = "HTTP/1.1 404 File Not Found\r\n" +

        "Content-Type: text/html\r\n" +

        "Content-Length: 23\r\n" +

        "\r\n" +

        "<h1>File Not Found</h1>";

      output.write(errorMessage.getBytes());

    }

    finally {

      if (fis!=null)

        fis.close();

    }

  }

  public PrintWriter getWriter() throws IOException {

    // autoflush is true, println() will flush,

    // but print() will not.

    writer = new PrintWriter(output, true);

    return writer;

  }

  //一样 部分代码 直接让Eclipse 自己主动生成就可以

}

试验一下

http://localhost:8080/servlet/PrimitiveServlet

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控制台显示

GET /servlet/PrimitiveServlet HTTP/1.1

Accept: image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash,

Accept-Language: zh-cn

User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; SV1)

Accept-Encoding: gzip, deflate

Host: localhost:8080

Connection: Keep-Alive

PrimitiveServlet*****D:\Java Code\UpLoad\webroot file:D:\Java Code\UpLoad\webroot\

from service

大家细致看看

Violets are blue. 这句话没有打印出来

大家看看Response类getWriter方法里的PrintWriter一行

上面的英文,我就不解释了

这个bug在以后的版本号中会改动

app2

上面的代码事实上还存在一个问题

在request部分中parseUri是private的,在这一节中这样事实上是能够的,但问题是这种方法有可能在外部类中使用,应该是public的。

假设改成public,问题又出现了

  public void service(ServletRequest request, ServletResponse response)

    throws ServletException, IOException {

    System.out.println("from service");

    Request r=(Request) request;

    System.out.println(r.parseUri("sdf"));

    PrintWriter out = response.getWriter();

    out.println("Hello. Roses are red.");

    out.print("Violets are blue.");

    out.flush();

  }

我把servlet类中的service改成上面的样子,大家看看,事实上request的parseUri方法在servlet里是不应该被使用的!

那怎么办?

第一种,将parseUri方法的public方法改成默认的訪问修饰符,包外的类就不能訪问了。

只是还有还有一种方式

门面模式!!

在上面的样例中,我们写的request实现了ServletRequest,我们能够再写一个类RequestFacade类让他也实现ServletRequest(response 类似)

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package ex02.pyrmont;

import java.io.IOException;

import java.io.BufferedReader;

import java.io.UnsupportedEncodingException;

import java.util.Enumeration;

import java.util.Locale;

import java.util.Map;

import javax.servlet.RequestDispatcher;

import javax.servlet.ServletInputStream;

import javax.servlet.ServletRequest;

public class RequestFacade implements ServletRequest {

  private ServletRequest request = null;

  public RequestFacade(Request request) {

    this.request = request;

  }

    public String getRemoteHost() {

    return request.getRemoteHost();

  }

  //省略对ServletRequest接口的实现

  //servletrequest接口的方法 在RequestFacade 内部实现时 都调用类的属性request来实现

  public void setCharacterEncoding(String encoding)

    throws UnsupportedEncodingException {

    request.setCharacterEncoding(encoding);

  }

}

再看看  ServletProcessor 改成例如以下

    Servlet servlet = null;

    RequestFacade requestFacade = new RequestFacade(request);

    ResponseFacade responseFacade = new ResponseFacade(response);

    try {

      servlet = (Servlet) myClass.newInstance();

      servlet.service((ServletRequest) requestFacade, (ServletResponse) responseFacade);

    }

    catch (Exception e) {

      System.out.println(e.toString());

    }

    catch (Throwable e) {

      System.out.println(e.toString());

    }

httpServer 也改成例如以下

 if (request.getUri().startsWith("/servlet/")) {

          ServletProcessor2 processor = new ServletProcessor2();

          processor.process(requestFacade , responseFacade );

        }

app1给servlet里面传递的參数实际上是Request类型的,有调用parseUri方法的危急。

app2给servlet里面传递的參数实际上是RequestFacade,它根本就没有parseUri方法,自然就安全了。

这篇文章中对书中的源代码有删减大家能够下载完整版本号的

深入剖析tomcat 源代码

http://down.51cto.com/data/486495