今天学习了servlet的数据库访问。
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 '' COMMENT '站点名称', `url` varchar(255) NOT NULL DEFAULT '', `alexa` int(11) NOT NULL DEFAULT '0' COMMENT 'Alexa 排名', `country` char(10) NOT NULL DEFAULT '' COMMENT '国家', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;
插入一些数据：
INSERT INTO `websites` VALUES ('1', 'Google', 'https://www.google.cm/', '1', 'USA'), ('2', '淘宝', 'https://www.taobao.com/', '13', 'CN'), ('3', '菜鸟教程', 'http://www.runoob.com', '5892', ''), ('4', '微博', 'http://weibo.com/', '20', 'CN'), ('5', 'Facebook', 'https://www.facebook.com/', '3', 'USA');
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>\n"; out.println(docType + "<html>\n" + "<head><title>" + title + "</title></head>\n" + "<body bgcolor=\"#f0f0f0\">\n" + "<h1 align=\"center\">" + title + "</h1>\n"); 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); } }