重新学习Servlet二

重新学习Servlet

public abstract class HttpServlet extends GenericServlet

package com.xh.test.api;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * Created by root on 17-11-12.
 */
public class MyHttpServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.service(req, resp);
        System.out.println(">>>MyHttpServlet.service");
        resp.getWriter().write("MyHttpServlet.service");
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //super.doGet(req, resp);
        System.out.println(">>>MyHttpServlet.doGet");
        resp.getWriter().write("MyHttpServlet.doGet");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //super.doPost(req, resp);
        System.out.println(">>>MyHttpServlet.doPost");
        resp.getWriter().write("MyHttpServlet.doPost");
    }
}

在restclient插件输入：http://localhost:8080/testservlet/1?id=100 ，切换方法GET,POST

输出是：

MyHttpServlet.doGetMyHttpServlet.service

MyHttpServlet.doPostMyHttpServlet.service

控制台：

>>>MyHttpServlet.doGet
>>>MyHttpServlet.service
>>>MyHttpServlet.doPost
>>>MyHttpServlet.service

PS:浏览器的请求过来，都要经过Servlet的service，如果自己不实现则走HttpServlet的。如果自己实现的，没有调用super.service(req, resp)，

则直接返回，如果调用了super.service(req, resp)，则HttpServlet会找当前类的对应的方法，如doGet，doPost，如果没有对应的实现，则抛异常，

如果实现了，就执行当前类的doGet，doPost方法，执行完后又返回到service方法，执行完返回给浏览器。

所以我们一般二者选其一实现（当然建议是doGet，doPost）。

    protected void service(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        String method = req.getMethod();

        if (method.equals(METHOD_GET)) {
            long lastModified = getLastModified(req);
            if (lastModified == -1) {
                // servlet doesn't support if-modified-since, no reason
                // to go through further expensive logic
                doGet(req, resp);
            } else {
                long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
                if (ifModifiedSince < lastModified) {
                    // If the servlet mod time is later, call doGet()
                    // Round down to the nearest second for a proper compare
                    // A ifModifiedSince of -1 will always be less
                    maybeSetLastModified(resp, lastModified);
                    doGet(req, resp);
                } else {
                    resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
                }
            }

        } else if (method.equals(METHOD_HEAD)) {
            long lastModified = getLastModified(req);
            maybeSetLastModified(resp, lastModified);
            doHead(req, resp);

        } else if (method.equals(METHOD_POST)) {
            doPost(req, resp);

        } else if (method.equals(METHOD_PUT)) {
            doPut(req, resp);

        } else if (method.equals(METHOD_DELETE)) {
            doDelete(req, resp);

        } else if (method.equals(METHOD_OPTIONS)) {
            doOptions(req,resp);

        } else if (method.equals(METHOD_TRACE)) {
            doTrace(req,resp);

        } else {
            //
            // Note that this means NO servlet supports whatever
            // method was requested, anywhere on this server.
            //

            String errMsg = lStrings.getString("http.method_not_implemented");
            Object[] errArgs = new Object[1];
            errArgs[0] = method;
            errMsg = MessageFormat.format(errMsg, errArgs);

            resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
        }
    }

    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        String protocol = req.getProtocol();
        String msg = lStrings.getString("http.method_get_not_supported");
        if (protocol.endsWith("1.1")) {
            resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        }
    }