Java EE-servlet API 三种主要的类

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上述的代码如下：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Enumeration;@WebServlet("/request")
public class RequestServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 下面这个操作也是必要的. 显式告诉浏览器, 你拿到的数据是 html.resp.setContentType("text/html");StringBuilder respBody=new StringBuilder();respBody.append(req.getProtocol());//使用 <br> 标签表示换行respBody.append("<br>");respBody.append(req.getMethod());respBody.append("<br>");respBody.append(req.getRequestURI());respBody.append("<br>");respBody.append(req.getContextPath());respBody.append("<br>");respBody.append(req.getQueryString());respBody.append("<br>");//Enumeration 枚举类型，每一个枚举类型都是一个键值对，即headers中包含多个键值对Enumeration<String> headers=req.getHeaderNames();while(headers.hasMoreElements()){//一开始的时候，并不指向第一个键值对的nameString header= headers.nextElement();//指向第一个键值对的namerespBody.append(header + ": "+req.getHeader(header));//getHeader:获取键值对的值respBody.append("<br>");}resp.getWriter().write(respBody.toString());}
}

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上述的代码如下：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/parameter1")
public class ParameterServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 约定, 客户端使用 query string 传递数据.// query string 形如: username=zhangsan&password=123String user_name=req.getParameter("username");String pass_word=req.getParameter("password");System.out.println("username"+":"+user_name);System.out.println("password"+":"+pass_word);resp.getWriter().write("ok");}
}

上述的代码如下：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/parameter2")
public class ParameterServlet2 extends HttpServlet {// 预期让客户端发送一个 POST 请求. 同时使用 form 格式的数据, 在 body 中把数据传递过来.// body 形如:// username=zhangsan&password=123@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String user_name=req.getParameter("username");String pass_word=req.getParameter("password");System.out.println("username :"+ user_name);System.out.println("password :"+ pass_word);resp.getWriter().write("okk");}
}

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上述过程的代码如下：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/status")
public class StatusServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//resp.setStatus(404);resp.setContentType("text/html;charset=utf8");resp.sendError(500);resp.getWriter().write("okkkk");}
}

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上述过程的代码如下：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/refresh")
public class RefreshServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//每2秒刷新一次resp.setHeader("refresh","2");resp.getWriter().write("time "+ System.currentTimeMillis());}
}

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上述过程的代码如下：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/redirect")
public class RedirectServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//resp.setStatus(302);//resp.setHeader("Location","http://www.baidu.com");resp.sendRedirect("http://www.baidu.com");}
}

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上述过程的代码如下：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/body")
public class BodyServlet extends HttpServlet {@Override//让服务器返回一个html的数据protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {resp.setContentType("text/html;charset=utf8");resp.getWriter().write("<div>你们好呀<div>");}
}