Servlet 数据库访问

本教程假定您已经了解了 JDBC 应用程序的工作方式。在您开始学习 Servlet 数据库访问之前，请访问 Java MySQL 连接来设置相关驱动及配置。

注意：

你可以下载本站提供的 jar 包：mysql-connector-java-5.1.39-bin.jar

在 java 项目中，只需要在 Eclipse 中引入 mysql-connector-java-5.1.39-bin.jar 就可以运行java项目。
但是在 Eclipse web 项目中，当执行 Class.forName("com.mysql.jdbc.Driver");时不会去查找驱动的。所以本实例中我们需要把 mysql-connector-java-5.1.39-bin.jar 拷贝到 tomcat 下 lib 目录。

从基本概念下手，让我们来创建一个简单的表，并在表中创建几条记录。

创建测试数据

接下来我们在 MySQL 中创建 RUNOOB 数据库，并创建 websites 数据表，表结构如下：

CREATE TABLE `websites` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` char(20) NOT NULL DEFAULT &qpos;&qpos; COMMENT &qpos;站点名称&qpos;,
  `url` varchar(255) NOT NULL DEFAULT &qpos;&qpos;,
  `alexa` int(11) NOT NULL DEFAULT &qpos;0&qpos; COMMENT &qpos;Alexa 排名&qpos;,
  `country` char(10) NOT NULL DEFAULT &qpos;&qpos; COMMENT &qpos;国家&qpos;,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

插入一些数据：

INSERT INTO `websites` VALUES (&qpos;1&qpos;, &qpos;Google&qpos;, &qpos;https://www.google.cm/&qpos;, &qpos;1&qpos;, &qpos;USA&qpos;), (&qpos;2&qpos;, &qpos;淘宝&qpos;, &qpos;https://www.taobao.com/&qpos;, &qpos;13&qpos;, &qpos;CN&qpos;), (&qpos;3&qpos;, &qpos;菜鸟教程&qpos;, &qpos;http://www.runoob.com&qpos;, &qpos;5892&qpos;, &qpos;&qpos;), (&qpos;4&qpos;, &qpos;微博&qpos;, &qpos;http://weibo.com/&qpos;, &qpos;20&qpos;, &qpos;CN&qpos;), (&qpos;5&qpos;, &qpos;Facebook&qpos;, &qpos;https://www.facebook.com/&qpos;, &qpos;3&qpos;, &qpos;USA&qpos;);

数据表显示如下：

访问数据库

下面的实例演示了如何使用 Servlet 访问 RUNOOB 数据库。

package com.runoob.test;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class DatabaseAccess
 */
@WebServlet("/DatabaseAccess")
public class DatabaseAccess extends HttpServlet {
    private static final long serialVersionUID = 1L;
    // JDBC 驱动名及数据库 URL
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
    static final String DB_URL = "jdbc:mysql://localhost:3306/RUNOOB";
    
    // 数据库的用户名与密码，需要根据自己的设置
    static final String USER = "root";
    static final String PASS = "123456"; 
    /**
     * @see HttpServlet#HttpServlet()
     */
    public DatabaseAccess() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Connection conn = null;
        Statement stmt = null;
        // 设置响应内容类型
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        String title = "Servlet Mysql 测试 - 菜鸟教程";
        String docType = "<!DOCTYPE html>
";
        out.println(docType +
        "<html>
" +
        "<head><title>" + title + "</title></head>
" +
        "<body bgcolor="#f0f0f0">
" +
        "<h1 align="center">" + title + "</h1>
");
        try{
            // 注册 JDBC 驱动器
            Class.forName("com.mysql.jdbc.Driver");
            
            // 打开一个连接
            conn = DriverManager.getConnection(DB_URL,USER,PASS);

            // 执行 SQL 查询
            stmt = conn.createStatement();
            String sql;
            sql = "SELECT id, name, url FROM websites";
            ResultSet rs = stmt.executeQuery(sql);

            // 展开结果集数据库
            while(rs.next()){
                // 通过字段检索
                int id  = rs.getInt("id");
                String name = rs.getString("name");
                String url = rs.getString("url");
    
                // 输出数据
                out.println("ID: " + id);
                out.println(", 站点名称: " + name);
                out.println(", 站点 URL: " + url);
                out.println("<br />");
            }
            out.println("</body></html>");

            // 完成后关闭
            rs.close();
            stmt.close();
            conn.close();
        } catch(SQLException se) {
            // 处理 JDBC 错误
            se.printStackTrace();
        } catch(Exception e) {
            // 处理 Class.forName 错误
            e.printStackTrace();
        }finally{
            // 最后是用于关闭资源的块
            try{
                if(stmt!=null)
                stmt.close();
            }catch(SQLException se2){
            }
            try{
                if(conn!=null)
                conn.close();
            }catch(SQLException se){
                se.printStackTrace();
            }
        }
       
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }
}

现在让我们来编译上面的 Servlet，并在 web.xml 文件中创建以下条目：

....
    <servlet>
        <servlet-name>DatabaseAccess</servlet-name>
        <servlet-class>com.runoob.test.DatabaseAccess</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>DatabaseAccess</servlet-name>
        <url-pattern>/TomcatTest/DatabaseAccess</url-pattern>
    </servlet-mapping>
....

现在调用这个 Servlet，输入链接：http://localhost:8080/TomcatTest/DatabaseAccess，将显示以下响应结果：