Java 学习札记01：使用JDBC连接MYSQL数据库

Java 学习笔记01：使用JDBC连接MYSQL数据库
JDBC是什么？

JDBC是一种用于执行SQL语句的Java API，可以为多种关系数据库提供统一访问，它由一组用JAVA编写的类和接口组成。说白了就和PHP的PDO一样，通过JDBC，JAVA可以使用相同的API接口来链接例如：MYSQL,SQLSERVER等不同类型的数据库。

package main;import java.sql.Connection;import java.sql.DriverManager;public class Mysql {public static void main(String arg[]) {try {Connection con = null; //定义一个MYSQL链接对象Class.forName("com.mysql.jdbc.Driver").newInstance(); //MYSQL驱动con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test", "root", "root"); //链接本地MYSQLSystem.out.print("yes");} catch (Exception e) {System.out.print("MYSQL ERROR:" + e.getMessage());}}}

Class.forName("com.mysql.jdbc.Driver").newInstance();  我们链接的是MYSQL数据库，所以需要一个MYSQL的数据库驱动，如果你的环境中木有安装，可以下载：mysql-connector-java-5.1.17-bin.jar JAR包，然后放进jdk1.6.0_37\jre\lib\ext 重启eclispe 就可以在JRE系统库中看到。con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test", "root", "root");  是链接数据库的语句，返回Connection con对象。参数格式：("jdbc:mysql://ip:端口/数据库名称", 用户名,密码)

package main;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.Statement;public class Mysql {/** * 入口函数 * @param arg */public static void main(String arg[]) {try {Connection con = null; //定义一个MYSQL链接对象Class.forName("com.mysql.jdbc.Driver").newInstance(); //MYSQL驱动con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test", "root", "root"); //链接本地MYSQLStatement stmt; //创建声明stmt = con.createStatement();//新增一条数据stmt.executeUpdate("INSERT INTO user (username, password) VALUES ('init', '123456')");ResultSet res = stmt.executeQuery("select LAST_INSERT_ID()");int ret_id;if (res.next()) {ret_id = res.getInt(1);System.out.print(ret_id);}} catch (Exception e) {System.out.print("MYSQL ERROR:" + e.getMessage());}}}

stmt.executeUpdate  INSERT DELETE UPDATE语句都用executeUpdate函数来操作stmt.executeQuery SELECT语句都用stmt.executeQuery函数来操作ResultSet res = stmt.executeQuery("select LAST_INSERT_ID()"); 查询最后插入数据的ID号，返回ResultSet res对象

package main;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.Statement;public class Mysql {/** * 入口函数 * @param arg */public static void main(String arg[]) {try {Connection con = null; //定义一个MYSQL链接对象Class.forName("com.mysql.jdbc.Driver").newInstance(); //MYSQL驱动con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test", "root", "root"); //链接本地MYSQLStatement stmt; //创建声明stmt = con.createStatement();//新增一条数据stmt.executeUpdate("INSERT INTO user (username, password) VALUES ('init', '123456')");ResultSet res = stmt.executeQuery("select LAST_INSERT_ID()");int ret_id;if (res.next()) {ret_id = res.getInt(1);System.out.print(ret_id);}//删除一条数据String sql = "DELETE FROM user WHERE id = 1";long deleteRes = stmt.executeUpdate(sql); //如果为0则没有进行删除操作，如果大于0，则记录删除的条数System.out.print("DELETE:" + deleteRes);//更新一条数据String updateSql = "UPDATE user SET username = 'xxxx' WHERE id = 2";long updateRes = stmt.executeUpdate(updateSql);System.out.print("UPDATE:" + updateRes);} catch (Exception e) {System.out.print("MYSQL ERROR:" + e.getMessage());}}}

删除和更新数据都使用stmt.executeUpdate函数。删除和更新数据都会返回一个Long的结果，如果为0，则删除或者更新失败，如果大于0则是操作的记录数

package main;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.ResultSetMetaData;import java.sql.Statement;public class Mysql {/** * 入口函数 * @param arg */public static void main(String arg[]) {try {Connection con = null; //定义一个MYSQL链接对象Class.forName("com.mysql.jdbc.Driver").newInstance(); //MYSQL驱动con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test", "root", "root"); //链接本地MYSQLStatement stmt; //创建声明stmt = con.createStatement();//新增一条数据stmt.executeUpdate("INSERT INTO user (username, password) VALUES ('init', '123456')");ResultSet res = stmt.executeQuery("select LAST_INSERT_ID()");int ret_id;if (res.next()) {ret_id = res.getInt(1);System.out.print(ret_id);}//删除一条数据String sql = "DELETE FROM user WHERE id = 1";long deleteRes = stmt.executeUpdate(sql); //如果为0则没有进行删除操作，如果大于0，则记录删除的条数System.out.print("DELETE:" + deleteRes);//更新一条数据String updateSql = "UPDATE user SET username = 'xxxx' WHERE id = 2";long updateRes = stmt.executeUpdate(updateSql);System.out.print("UPDATE:" + updateRes);//查询数据并输出String selectSql = "SELECT * FROM user";ResultSet selectRes = stmt.executeQuery(selectSql);while (selectRes.next()) { //循环输出结果集String username = selectRes.getString("username");String password = selectRes.getString("password");System.out.print("\r\n\r\n");System.out.print("username:" + username + "password:" + password);}} catch (Exception e) {System.out.print("MYSQL ERROR:" + e.getMessage());}}}

查询语句使用stmt.executeQuery函数

rs.absolute() //绝对位置，负数表示从后面数

rs.first()第一条

rs.last()最后一条

rs.previoust()前一条

rs.next()后一条

rs.beforeFirst()第一条之前

rs.afterLast()最后之后

rs.isFirst(),rs.isLast(),rs.isBeforeFirst(),rs.isAfterLast