[javaweb]javaweb中servlet的使用详解

本篇文章分享[javaweb]javaweb中servlet的使用详解，对你有帮助的话记得收藏一下，看Java资料网收获更多编程知识

servlet

sun公司提供两种实现类：

1.实现servlet接口

2.继承Httpservlet

• sun公司用来开发动态web的一门技术
• sun在这些API中提供了一个接口叫servlet，如果你想开发一个servlet程序，只需要完成两个小步骤。
  • 编写一个类，实现servlet类接口
  • 把开发好的java类部署到web服务器中

把实现了servlet接口的程序叫做servlet

创建一个helloservlet

导入maven依赖：

<dependencies>
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.11</version>
    <scope>test</scope>
  </dependency>

  <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
  <dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.1.0</version>

  </dependency>

  <dependency>
    <groupId>javax.servlet.jsp</groupId>
    <artifactId>javax.servlet.jsp-api</artifactId>
    <version>2.3.2-b01</version>
  </dependency>
</dependencies>

敲一个servlet

package com.javaweb;

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

/**
 * @author panglili
 * @create 2022-07-19-8:18
 */
public class HelloServlet extends HttpServlet {
    //由于get和post只是请求的方式不一样，因此只需要实现一个，在另一个里面调用
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("******doget");
        PrintWriter writer = resp.getWriter();
        writer.print("hello,servlet");
    }

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

注册在web上

<servlet>
  <servlet-name>hello</servlet-name>
  <servlet-class>com.javaweb.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>hello</servlet-name>
  <url-pattern>/add</url-pattern>
</servlet-mapping>

6.servletContext

web容器在启动的时候，会为每个web程序都创建一个servletcontext对象，代表当前web应用。全局唯一！

• 可以实现各个servlet之间的通信，统一的管理所有servlet的数据（一般不用此方法，增加浏览器负担）。
• servletcontext:调用servlet实现数据共享

测试一下：

（1）创建一个servlet使用context设置属性

package com.javaweb.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;

/**
 * @author panglili
 * @create 2022-07-19-8:18
 */
public class HelloServlet extends HttpServlet {
    //由于get和post只是请求的方式不一样，因此只需要实现一个，在另一个里面调用
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {


        ServletContext context = this.getServletContext();
        String username="ssss";
        context.setAttribute("username",username);
        System.out.println("******doget");

    }

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

（2）创建另一个servlet使用context获取属性值

package com.javaweb.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;

/**
 * @author panglili
 * @create 2022-07-19-16:28
 */
public class getServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();

        String username =(String) context.getAttribute("username");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html");
        resp.getWriter().print(username);
    }

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

（3）然后配置servlet在web中就可以在网页访问了

<servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>com.javaweb.servlet.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
</servlet-mapping>

<servlet>
    <servlet-name>getc</servlet-name>
    <servlet-class>com.javaweb.servlet.getServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>getc</servlet-name>
    <url-pattern>/getc</url-pattern>
</servlet-mapping>

（4）在网页请求getc可以拿到hello的属性值

• servletcontext获取web初始化参数

（1）web初始化数据

<context-param>
    <param-name>url</param-name>
    <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
</context-param>

（2）servlet中获取

package com.javaweb.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;

/**
 * @author panglili
 * @create 2022-07-19-17:02
 */
public class ServletDemo extends HttpServlet {
    //由于get和post只是请求的方式不一样，因此只需要实现一个，在另一个里面调用
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        resp.getWriter().print(url);

        System.out.println("******doget");

    }

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

（3）网页数据

• servletcontext：实现页面请求转发：

（1）写请求转发的servlet

此请求被转发到getIni

package com.javaweb.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;

/**
 * @author panglili
 * @create 2022-07-19-17:02
 */
public class ServletDemo2 extends HttpServlet {
    //由于get和post只是请求的方式不一样，因此只需要实现一个，在另一个里面调用
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        context.getRequestDispatcher("/getIni").forward(req,resp);

        System.out.println("******doget");

    }

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

（2）web配置

请求demo2

<servlet>
    <servlet-name>demo2</servlet-name>
    <servlet-class>com.javaweb.servlet.ServletDemo2</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>demo2</servlet-name>
    <url-pattern>/demo2</url-pattern>
</servlet-mapping>

（3）网页实现

返回的是getIni数据

文章来源:https://www.cnblogs.com/lumanmanqixiuyuanxi/p/16512657.html
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