JAVA---Servlet

本文主要是介绍JAVA---Servlet，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

package servlet;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

/**
 *通过实现Servlet接口的方式创建Servlet
 * @create 2022-04-21 20:52
 */
public class HelloServlet implements Servlet {

    public HelloServlet(){
        System.out.println("1 构造器方法");
    }
    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        System.out.println("2 init初始化方法");
        //1.可以获取Servlet程序的别名servlet-name的值
        System.out.println("HelloServlet程序的别名是："+servletConfig.getServletName());
        //2.获取初始化参数init-param
        System.out.println("初始化参数username的值是："+servletConfig.getInitParameter("username"));
        System.out.println("初始化参数url的值是："+servletConfig.getInitParameter("url"));
        //3.获取ServletContext对象
        System.out.println(servletConfig.getServletContext());
        
    }

    @Override
    public ServletConfig getServletConfig() {
        return null;
    }

    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        System.out.println("servlet is access");
        //类型转换（因为HttpServletRequest有getMethod()方法）
        HttpServletRequest httpServletRequest= (HttpServletRequest) servletRequest;
        //获取请求的方式
        String method = httpServletRequest.getMethod();
        
        if("GET".equals(method)){
            doGet();
        } else if("POST".equals(method)){
            doPost();
        }

    }
    
    /*
        做Get请求的操作
        
     */
    public void doGet(){
        System.out.println("get请求");
    }
    
    /*
        做post请求的操作
     */
    public void doPost(){
        System.out.println("post请求");
    }

    @Override
    public String getServletInfo() {
        return null;
    }

    @Override
    public void destroy() {
        System.out.println("4. destroy销毁方法");
    }
}

package servlet;

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

/**
 * 通过继承HttpServlet类的方式创建Servlet
 * @create 2022-04-22 22:28
 */
public class HelloServlet2 extends HttpServlet {
    /**
     * 在get请求的时候调用
     * @param req
     * @param resp
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("HelloServlet2 的doGet方法");

        ServletConfig servletConfig = getServletConfig();
        System.out.println(servletConfig);
        
        //获取初始化参数init-param
        System.out.println("初始化参数username的值是："+servletConfig.getInitParameter("username"));
        System.out.println("初始化参数url的值是："+servletConfig.getInitParameter("url"));

    }


    /**
     * 处理post请求的时候调用
     * @param req
     * @param resp
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("HelloServlet2的doPost方法");
    }
    

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        System.out.println("重写了init初始化方法，做了一些工作");
    }
}

package servlet;

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

/**
 * 
 * @create 2022-04-23 10:54
 */
public class ContextServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.获取web.xml中配置的上下文参数context-param
        ServletContext context = getServletConfig().getServletContext();

        System.out.println("context-param参数username的值是："+context.getInitParameter("username"));
        System.out.println("context-param参数password的值是："+context.getInitParameter("password"));
        
        //获取当前的工程路径，格式：/工程路径
        System.out.println("当前工程路径"+context.getContextPath());
        
        //获取工程部署后在服务器硬盘上的绝对路径
        /*
            / 斜杠被服务器解析地址为:http://ip:port/工程名/       映射到idea代码的web目录
            
         */
        System.out.println("工程部署的路径是："+context.getRealPath("/"));
        
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doGet");
    }
}

package servlet;

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

/**
 * @create 2022-04-23 11:25
 */
public class ContextServlet1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       //获取servletContext对象
        ServletContext servletContext = getServletContext();
        System.out.println(servletContext);
        System.out.println("保存之前："+servletContext.getAttribute("key1"));
        servletContext.setAttribute("key1","value1");
        System.out.println("保存之后："+servletContext.getAttribute("key1"));
        
    }
}

package servlet;

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

/**
 * @create 2022-04-23 11:40
 */
public class ContextServlet2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = getServletContext();
        System.out.println(servletContext);
        System.out.println("ContextServlet2获取ContextServlet1中的key1的值为："+servletContext.getAttribute("key1"));
        
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">
    
    <!--context-param是上下文参数（属于整个web工程）-->
    <context-param>
        <param-name>username</param-name>
        <param-value>context</param-value>
    </context-param>
    
    <context-param>
        <param-name>password</param-name>
        <param-value>123456</param-value>
    </context-param>
    
    
    <!--servlet标签给Tomcat配置Servlet程序 -->
    <servlet>
        <!--servlet-name标签给servlet程序起一个别名（一般是类名）-->
        <servlet-name>HelloServlet</servlet-name>
        <!--servlet-class是Servlet程序的全类名-->
        <servlet-class>servlet.HelloServlet</servlet-class>
        <!--init-param是初始化参数-->
        <init-param>
            <!--参数名-->
            <param-name>username</param-name>
            <!--是参数值-->
            <param-value>root</param-value>
        </init-param>
        <init-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql://localhost:3306/test</param-value>
        </init-param>
    </servlet>
    <!--servlet-mapping标签给servlet程序配置访问地址-->
    <servlet-mapping>
        <!--servlet-name标签的作用是告诉服务器，当前配置的地址要给哪个Servlet程序使用-->
        <servlet-name>HelloServlet</servlet-name>
        <!--
            url-pattern标签配置访问地址
            /斜杠在服务器解析的时候，表示地址为：http://ip:port/工程路径
            /hello表示地址为：http://ip:port/工程路径/hello
        -->
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
    
    <servlet>
        <servlet-name>HelloServlet2</servlet-name>
        <servlet-class>servlet.HelloServlet2</servlet-class>
        
        <init-param>
            <param-name>username</param-name>
            <param-value>root</param-value>
        </init-param>
        <init-param>
            <param-name>url</param-name>
            <param-value>this is HelloServlet2</param-value>
        </init-param>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>HelloServlet2</servlet-name>
        <url-pattern>/hello2</url-pattern>
    </servlet-mapping>
    
    
    <servlet>
        <servlet-name>ContextServlet</servlet-name>
        <servlet-class>servlet.ContextServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ContextServlet</servlet-name>
        <url-pattern>/context</url-pattern>
    </servlet-mapping>
    
    
    <servlet>
        <servlet-name>ContextServlet1</servlet-name>
        <servlet-class>servlet.ContextServlet1</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ContextServlet1</servlet-name>
        <url-pattern>/context1</url-pattern>
    </servlet-mapping>
    
    
    <servlet>
        <servlet-name>ContextServlet2</servlet-name>
        <servlet-class>servlet.ContextServlet2</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ContextServlet2</servlet-name>
        <url-pattern>/context2</url-pattern>
    </servlet-mapping>
    
</web-app>

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