JDBC工具类连接数据库测试

测试代码

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

import com.jdbcutils.JDBCUtils;

public class JDBCDemo2 {
	public void select(){
		Connection conn = null;
		PreparedStatement pstmt = null;
		ResultSet rs = null;
		try{
			// 获取连接
			conn = JDBCUtils.getConnection();
			// 编写SQL:
			String sql = "select * from user";
			// 预编译SQL:
			pstmt = conn.prepareStatement(sql);
			// 获取结果集
			rs = pstmt.executeQuery();
			// 遍历
			while(rs.next()){
				System.out.println(rs.getInt("id")+" "+rs.getString("username")+" "+rs.getString("password")+" "+rs.getString("nickname"));
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally{
			// 关闭资源
			JDBCUtils.release(rs, pstmt, conn);
		}
	}
}

package com.jdbcutils;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Properties;

public class JDBCUtils {
	private static final String driverClassName;
	private static final String url;
	private static final String username;
	private static final String password;
	static{
		Properties Properties = new Properties();
		try {
			Properties.load(new FileInputStream("src/db.properties"));
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		driverClassName = Properties.getProperty("driverClassName");
		url = Properties.getProperty("url");
		username = Properties.getProperty("username");
		password = Properties.getProperty("password");
	}
	//加载驱动
	public static void loadDriver(){
		try {
			Class.forName(driverClassName);
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}
	//获取连接
	public static Connection getConnection(){
		Connection conn = null;
		try {
			loadDriver();
			conn = DriverManager.getConnection(url, username, password);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return conn;
	}
	public static void release(Statement stmt,Connection conn){
		if(stmt != null){
			try {
				stmt.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
			stmt = null;
		}
		if(conn != null){
			try {
				conn.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
			conn = null;
		}
	}
	public static void release(ResultSet rs,Statement stmt,Connection conn){
		if(rs != null){
			try {
				rs.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
			rs = null;
		}
		if(stmt != null){
			try {
				stmt.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
			stmt = null;
		}
		if(conn != null){
			try {
				conn.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
			conn = null;
		}
	}
}

db.properties

    driverClassName=com.mysql.jdbc.Driver
    url=jdbc:mysql:///web_test3
    username=root
    password=123

SQL建表语句

create database web_test3;
use web_test3;
create table user(
	id int primary key auto_increment,
	username varchar(20),
	password varchar(20),
	nickname varchar(20),
	age int
);
insert into user values (null,'aaa','123','小丽',34);
insert into user values (null,'bbb','123','大王',32);
insert into user values (null,'ccc','123','小明',28);
insert into user values (null,'ddd','123','大黄',21);