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Servlet 數據庫訪問

Servlet 數據庫訪問

本教程假定您已經了解了 JDBC 應用程序的工作方式。在您開始學習 Servlet 數據庫訪問之前,請訪問 Java MySQL 連接 來設置相關驅動及配置。

注意:

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

在 java 項目中,只需要在 Eclipse 中引入 mysql-connector-java-5.1.39-bin.jar 就可以運行java項目。

但是在 Eclipse web 項目中,當執行 Class.forName("com.mysql.jdbc.Driver");時 不會去查找驅動的。所以本實例中我們需要把 mysql-connector-java-5.1.39-bin.jar 拷貝到 tomcat 下 lib 目錄。

從基本概念下手,讓我們來創建一個簡單的表,併在表中創建幾條記錄。


創建測試數據

接下來我們在 MySQL 中創建 RUNOOB 數據庫,併創建 websites 數據表,表結構如下:

CREATE TABLE `websites` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` char(20) NOT NULL DEFAULT '' COMMENT '站點名稱',
  `url` varchar(255) NOT NULL DEFAULT '',
  `alexa` int(11) NOT NULL DEFAULT '0' COMMENT 'Alexa 排名',
  `country` char(10) NOT NULL DEFAULT '' COMMENT '國家',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

插入一些數據:

INSERT INTO `websites` VALUES ('1', 'Google', 'https://www.google.cm/', '1', 'USA'), ('2', '淘寶', 'https://www.taobao.com/', '13', 'CN'), ('3', '教程', 'http://www.sharebody.com', '5892', ''), ('4', '微博', 'http://weibo.com/', '20', 'CN'), ('5', 'Facebook', 'https://www.facebook.com/', '3', 'USA');

數據表顯示如下:



訪問數據庫

下面的實例演示了如何使用 Servlet 訪問 RUNOOB 數據庫。

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 驅動名及數據庫 URL
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
    static final String DB_URL = "jdbc:mysql://localhost:3306/RUNOOB";
    
    // 數據庫的用戶名與密碼,需要根據自己的設置
    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;
        // 設置響應內容類型
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        String title = "Servlet Mysql 測試 - 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{
            // 注冊 JDBC 驅動器
            Class.forName("com.mysql.jdbc.Driver");
            
            // 打開一個連接
            conn = DriverManager.getConnection(DB_URL,USER,PASS);
            // 執行 SQL 查詢
            stmt = conn.createStatement();
            String sql;
            sql = "SELECT id, name, url FROM websites";
            ResultSet rs = stmt.executeQuery(sql);
            // 展開結果集數據庫
            while(rs.next()){
                // 通過字段檢索
                int id  = rs.getInt("id");
                String name = rs.getString("name");
                String url = rs.getString("url");
    
                // 輸出數據
                out.println("ID: " + id);
                out.println(", 站點名稱: " + name);
                out.println(", 站點 URL: " + url);
                out.println("<br />");
            }
            out.println("</body></html>");
            // 完成後關閉
            rs.close();
            stmt.close();
            conn.close();
        } catch(SQLException se) {
            // 處理 JDBC 錯誤
            se.printStackTrace();
        } catch(Exception e) {
            // 處理 Class.forName 錯誤
            e.printStackTrace();
        }finally{
            // 最後是用於關閉資源的塊
            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);
    }
}

現在讓我們來編譯上面的 Servlet,併在 web.xml 文件中創建以下條目:

....
    <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>
....

現在調用這個 Servlet,輸入鏈接:http://localhost:8080/TomcatTest/DatabaseAccess,將顯示以下響應結果:

北斗有巢氏 有巢氏北斗