javaWeb之Servlet

Servlet介绍

• Servlet是sun 公司提供的一门用于开发动态web资源的技术。
• 用户若想开发一个动态Web资源（即开发一个java程序想向浏览器去输出数据），需要完成2个步骤：
  1.编写一个java类，实现servlet接口
  2.把开发好的Java类部署到Web服务器中
• 通常我们把实现了servlet接口的java程序称之为Servlet

Servlet运行过程

Servlet实现类

使用Idea开发Servlet

Servlet映射路径问题

1.一般情况下我们都会指定一个URL ， 一个URL对应一个请求
2.通配问题
/* ：不报错
*.do

转发和重定向的区别 （面试常见题：笔试）

重定向：服务器告诉客户端，你去请求另外一个地址；客户端行为

• 地址栏会变
• 不能携带参数

转发：服务器自己转发到服务器上的另一个请求； 服务器行为

• 地址栏不会变
• 可以携带参数
  将这个请求，转换到另一个地址；

ServletContext

图示：

案例一：
src：

package com.kuang.servlet;

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

public class ServletTest01 extends HttpServlet {

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

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("我接受到你的请求了");
        }
        }

package com.kuang.servlet;

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;

public class SetvletTest02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        /*
        //告诉浏览器，我们响应的东西使用html解析；
        resp.setContentType("text/html");
        resp.setCharacterEncoding("UTF-8");
        //通过响应给客户端返回一个字符串
        PrintWriter writer = resp.getWriter();
        writer.print("你好！");
        writer.print("<h1>Hello,Servlet!</h1>");
        */
        resp.sendRedirect("index.jsp");

    }

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

}

package com.kuang.servlet;

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

public class Failed extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.sendRedirect("404.jsp");
        System.out.println("123123123");
    }
}

web下：404和index.jsp
web.xml:

<?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_4_0.xsd"
         version="4.0">


    <servlet>
        <servlet-name>ServletTest01</servlet-name>
        <servlet-class>com.kuang.servlet.ServletTest01</servlet-class>
    </servlet>

    <servlet>
        <servlet-name>Test02</servlet-name>
        <servlet-class>com.kuang.servlet.SetvletTest02</servlet-class>
    </servlet>

    <servlet>
        <servlet-name>404</servlet-name>
        <servlet-class>com.kuang.servlet.Failed</servlet-class>
    </servlet>




    <!--
        关于请求路径问题：
        localhost:8080/项目名/请求的路径
        localhost:8080/servlet01/
    -->
    <servlet-mapping>
        <servlet-name>ServletTest01</servlet-name>
        <url-pattern>/test01</url-pattern>
    </servlet-mapping>
    <!--
        /*
        /*.do
        /item/马云
   【注意】尽量在请求的URL中不要使用中文；
    -->

    <!--
        RestFul风格
        localhost:8080/项目名/第一级（第一个参数）/第二级（第二个参数）/...
        localhost:8080/项目名/hello?username=admin&password=123456
        localhost:8080/项目名/hello/admin/123456
    -->

    <servlet-mapping>
        <servlet-name>Test02</servlet-name>
        <url-pattern>/test02</url-pattern>
    </servlet-mapping>

    <servlet-mapping>
        <servlet-name>404</servlet-name>
        <url-pattern>*.do</url-pattern>
    </servlet-mapping>


</web-app>

案例二：
src:

package com.kuang.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;


public class ServletDemo01 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //通过servlet对象可以获取一个ServletContext；
        ServletContext context = this.getServletContext();

        String username = "小学生";//可以通过JDBC去读取；
        //setAttribute ：设置一个属性；（属性名，属性值）
        context.setAttribute("name",username);
        response.setCharacterEncoding("utf-8");
        response.getWriter().print("设置name成功："+username);
    }
}

package com.kuang.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;

public class ServletDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }

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

        ServletContext context = this.getServletContext();
        String name = (String) context.getAttribute("name");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print("我们获取到的ServletDemo01信息为："+name);

    }
}

web.xml:

<?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_4_0.xsd"
         version="4.0">
    
    <servlet>
        <servlet-name>Demo01</servlet-name>
        <servlet-class>com.kuang.servlet.ServletDemo01</servlet-class>
    </servlet>

    <servlet>
        <servlet-name>Demo02</servlet-name>
        <servlet-class>com.kuang.servlet.ServletDemo02</servlet-class>
    </servlet>

    <!--=====================================================-->
    
    <servlet-mapping>
        <servlet-name>Demo01</servlet-name>
        <url-pattern>/q1</url-pattern>
    </servlet-mapping>

    <servlet-mapping>
        <servlet-name>Demo02</servlet-name>
        <url-pattern>/q2</url-pattern>
    </servlet-mapping>

</web-app>

案例三：通过servletcontext读取网站的配置信息

新建一个properties文件:

driver=com.mysql.jdbc.Driver
username=root
password=123456
url=jdbc:mysql://localhost:3306/smbms

编写servlet类:

package com.kuang.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;

//读取properties配置文件
public class ServletDemo03 extends HttpServlet {

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

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //读取配置文件

        //1.获得配置文件的路径
        String realPath = this.getServletContext().getRealPath("/WEB-INF/classes/resources/database.properties");
        System.out.println("取得的路径为："+realPath);

        Properties properties = new Properties();
        FileInputStream is = new FileInputStream(realPath);

        properties.load(is);//把文件流加载到配置文件的对象中；

        String driver = properties.getProperty("driver");
        String username = properties.getProperty("username");
        String password = properties.getProperty("password");
        String url = properties.getProperty("url");


        //响应到网页
        resp.getWriter().println(driver);
        resp.getWriter().println(username);
        resp.getWriter().println(password);
        resp.getWriter().println(url);

        //=======================================
        System.out.println(driver);
        System.out.println(username);
        System.out.println(password);
        System.out.println(url);



    }
}

配置web.xml文件：

<servlet>
    <servlet-name>Demo03</servlet-name>
    <servlet-class>com.kuang.servlet.ServletDemo03</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>Demo03</servlet-name>
    <url-pattern>/q3</url-pattern>
</servlet-mapping>

访问查看：

localhost：8080/demo02/q3

乱码问题解决方案：

• 所有能设置编码的地方都统一设置 ： 数据库，数据库字段，Servlet程序，请求，响应 ， 前端，浏览器。