创建servlet的三种方式 1.实现 servlet接口 2.继承GenericServlet类 3.继承HttpServlet类

程序员文章站 2022-05-23 18:30:24

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创建servlet的三种方式

1.实现 servlet接口

package servlet_mvn_jd2007;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class FirstServlet implements Servlet{

	public FirstServlet() {
		System.out.println("FirstServlet 构造器。。。。");
	}
	
	@Override
	public void destroy() {
		System.out.println("destory.....删除方法");
		
	}

	@Override
	public ServletConfig getServletConfig() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public String getServletInfo() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public void init(ServletConfig arg0) throws ServletException {
		System.out.println("FirstServlet init......初始化方法init");
		
	}

	@Override
	public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
		System.out.println("service----------------");
		res.setContentType("text/html;charset=UTF-8");
		double r = Math.random();
		PrintWriter pw = res.getWriter();
		pw.println("<html>");
			pw.println("<head>");
				pw.println("<meta charset='UTF-8'>");
				pw.println("<title>First Servlet</title>");
			pw.println("</head>");
			pw.println("<body>");
				pw.println(
						"<font color='green' size='7'>随机数为:"+r+"</font>");
			pw.println("</body>");
	   pw.println("</html>");
	}

}

注意:三种方法都要在web.xml中配置<servlet>信息才可以运行,servlet3.0以后也可以通过写注解的方式来实现,第三种方法见

<servlet>中的顺序必须下面的一样

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>servlet_jd2007</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
  <!-- 两个name必须相同,class里面时该类的权限类名,URL除通配符*外都必须以/开头 -->
    <servlet-name>first</servlet-name>
    <servlet-class>servlet_mvn_jd2007.FirstServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>first</servlet-name>
    <url-pattern>/first.do</url-pattern>
  </servlet-mapping>

<!--第二种方法的配置信息-->
<servlet>
    <servlet-name>Second</servlet-name>
    <servlet-class>servlet_mvn_jd2007.SecondServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Second</servlet-name>
    <url-pattern>/second.do</url-pattern>
  </servlet-mapping>
</web-app>

2.继承GenericServlet类

package servlet_mvn_jd2007;

import java.io.IOException;
import java.io.PrintWriter;

import javax.security.auth.Refreshable;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class SecondServlet extends GenericServlet{

	private static final long serialVersionUID = 1L;

	public SecondServlet() {
		System.out.println("SecondServlet Construtor....");
	}
	@Override
	public void init() throws ServletException {
		System.out.println("SecondServlet init ....");
	}
	@Override
	public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
		res.setContentType("application/xml;charset+UTF-8");
		PrintWriter pw = res.getWriter();
		pw.println("<students>");
			pw.println("<student sno='s1'>");
				pw.println("<name>briup1</name>");
				pw.println("<age>18</age>");
			pw.println("</student>");
			pw.println("<student sno='s2'>");
				pw.println("<name>briup2</name>");
				pw.println("<age>19</age>");
			pw.println("</student>");
		pw.println("</students>");
		pw.flush();
	}

}

3.继承HttpServlet类

package servlet_mvn_jd2007;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileInputStream;
import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//通过注解的方式,就不需要在web.xml中配置信息了,name可以省略.推荐使用该方法
//@WebServlet(name = "three",urlPatterns = {"/three.do"})
@WebServlet("/three.do")
public class ThreeServlet extends HttpServlet{

	private static final long serialVersionUID = 1L;
	
	public ThreeServlet() {
		System.out.println("Threeservlet constructor..");
	}
	@Override
	public void init() throws ServletException {
		System.out.println("ThreeServlet init...");
	}
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		System.out.println("doGet.....threServlet..");
		resp.setContentType("image/jpeg");
		try(BufferedInputStream bis = new BufferedInputStream(new FileInputStream("F:\\A图片\\1.jpg"));
				BufferedOutputStream bos = new BufferedOutputStream(resp.getOutputStream());
				) {
			byte[] b = new byte[1024];
			int len = 0;
			while((len=bis.read(b))!=-1) {
				bos.write(b, 0, len);
			}
			bos.flush();
			
		} catch (Exception e) {
			e.printStackTrace();
		}
		
	}
	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		doGet(req, resp);
	}
	@Override
	public void destroy() {
		System.out.println("ThreeServlet destory...");
		System.out.println("");
	}

}

注意:在maven项目中要在pom.xml中配置一些信息才可以写servlet

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.briup.jd2007</groupId>
  <artifactId>servlet_mvn_jd2007</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>war</packaging>
  
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>
  
    <dependencies>
    <!-- 引入servlet3.1的依赖 -->
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
        <scope>provided</scope>
    </dependency>
    
    <!-- 引入jstl的依赖，jsp页面中会使用到 -->
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version></dependency>
    </dependencies>
</project>

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