HttpServlet

什么是HttpServlet

sun公司为Servlet定义了一个抽象类HttpServlet

HttpServlet指能够处理HTTP请求的servlet，它在原有Servlet接口上添加了一些与HTTP协议处理方法，它比Servlet接口的功能更为强大。因此开发人员在编写Servlet时，通常应继承这个类，而避免直接去实现Servlet接口。

HttpServlet在实现Servlet接口时，覆写了service方法，该方法体内的代码会自动判断用户的请求方式，如为GET请求，则调用HttpServlet的doGet方法，如为Post请求，则调用doPost方法。因此，开发人员在编写Servlet时，通常只需要覆写doGet或doPost方法，而不要去覆写service方法

封装的service方法可以看下，不需要记

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

if (method.equals("GET")) {
long lastModified = getLastModified(req);
if (lastModified == -1L)
{
doGet(req, resp);
} else {
long ifModifiedSince = req.getDateHeader("If-Modified-Since");
if (ifModifiedSince < lastModified)
{
maybeSetLastModified(resp, lastModified);
doGet(req, resp);
} else {
resp.setStatus(304);
}
}
}
else if (method.equals("HEAD")) {
long lastModified = getLastModified(req);
maybeSetLastModified(resp, lastModified);
doHead(req, resp);
}
else if (method.equals("POST")) {
doPost(req, resp);
}
else if (method.equals("PUT")) {
doPut(req, resp);
}
else if (method.equals("DELETE")) {
doDelete(req, resp);
}
else if (method.equals("OPTIONS")) {
doOptions(req, resp);
}
else if (method.equals("TRACE")) {
doTrace(req, resp);
}
else
{
String errMsg = lStrings.getString("http.method_not_implemented");
Object[] errArgs = new Object[1];
errArgs[0] = method;
errMsg = MessageFormat.format(errMsg, errArgs);

resp.sendError(501, errMsg);
}
}

HttpServlet的实现

package com.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Servlet2 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
doPost(req, resp);
}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {

}
}