java Servlet实现及转发、重定向

一、实现Servlet接口

package com.example.demo.servlet;

import javax.servlet.*;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import java.io.IOException;

@WebServlet(name = "myServlet", urlPatterns = "/myServlet",initParams = {
        @WebInitParam(name = "p1", value = "param1"),
        @WebInitParam(name = "p2", value = "param2")
})
public class MyServlet implements Servlet {

    private  ServletConfig config;

    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        System.err.println("初始化Servlet。。。");
        this.config=servletConfig;
        String name=config.getServletName();
        System.err.println("Servlet别名："+name);
        System.err.println("初始化参数1："+config.getInitParameter("p1"));
        System.err.println("初始化参数2："+config.getInitParameter("p2"));
    }

    @Override
    public ServletConfig getServletConfig() {
        System.err.println("获取Servlet配置。。。");
        return config;
    }

    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        System.err.println("处理业务。。。");
        //防止中文乱码
        servletResponse.setContentType("text/html;charset=utf-8");
        //写出到浏览器
        servletResponse.getWriter().write("myServlet...厉害了");
    }

    @Override
    public String getServletInfo() {
        System.err.println("获取Servlet信息。。。");
        return "我是Servlet信息";
    }

    @Override
    public void destroy() {
        System.err.println("销毁Servlet。。。");
    }
}

运行项目，请求路径http://localhost:81/myServlet。浏览器结果：

控制台打印结果：

初始化Servlet。。。
Servlet别名：myServlet
初始化参数1：param1
初始化参数2：param2
处理业务。。。

二、继承HttpServlet类

package com.example.demo.servlet;

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(name = "firstServlet", urlPatterns = "/firstServlet")
public class FirstServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //防止中文乱码
        response.setContentType("text/html;charset=utf-8");
        //写出到浏览器
        response.getWriter().write("firstServlet...厉害了");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }
}

运行项目，访问http://localhost:81/firstServlet。浏览器结果：

三、重定向和转发

1、重定向

package com.example.demo.servlet;

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(name = "firstServlet", urlPatterns = "/firstServlet")
public class FirstServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //重定向到http://localhost:81/myServlet(下面两句话是一个意思)
//        response.sendRedirect("myServlet");
        response.sendRedirect("http://localhost:81/myServlet");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }
}

请求http://localhost:81/firstServlet。看开发者工具，发现进行了两次请求。先请求firstServlet，然后重新请求myServlet。

控制台：

初始化Servlet。。。
Servlet别名：myServlet
初始化参数1：param1
初始化参数2：param2
处理业务。。。
处理业务。。。

2、转发

package com.example.demo.servlet;

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(name = "firstServlet", urlPatterns = "/firstServlet")
public class FirstServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //转发到http://localhost:81/myServlet
        request.getRequestDispatcher("myServlet").forward(request,response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }
}

请求http://localhost:81/firstServlet。看开发者工具，发现只请求了firstServlet，但请求返回的内容是myServlet的。

响应内容：

重定向可以访问外部资源，转发不可以。下面重定向到百度。

package com.example.demo.servlet;

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(name = "firstServlet", urlPatterns = "/firstServlet")
public class FirstServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //重定向到百度
        response.sendRedirect("https://www.baidu.com/");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }
}

浏览器结果