一般JDBC的常见写法（附懒汉式 && 饿汉式）

首先在建个DbUtil文件，里面返回Connection、关闭方法等，如下所示：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

/**
 * 数据库工具类(获取连接、释放资源)
 *
 * @author YUSHIBUJUE
 *
 */
public abstract class DbUtil {

    // 只需要执行一次
    static{
        try {
            System.out.println("注册数据库驱动......");
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            throw new RuntimeException("注册数据库驱动出现异常:"+e.getMessage());
        }
    }
    /**
     * 获取一个连接对象
     * @return
     */
    public static Connection getConn() {
        String url = "jdbc:mysql://localhost/flightsystem?characterEncoding=GBK";
        try {
            return DriverManager.getConnection(url, "root", "root");
        } catch (SQLException ex1) {
            throw new RuntimeException("无法获取连接,原因:"+ex1.getMessage());
        }
    }


    public static void free(ResultSet rs, Statement st, Connection conn) {
        try {
            if (null != rs) {
                rs.close();
                System.out.println("ResultSet已关闭！");
            }
        } catch (SQLException e) {
            throw new RuntimeException("关闭ResultSet出现异常:" + e.getMessage());
        } finally {
            try {
                if (null != st) {
                    st.close();
                    System.out.println("Statement已关闭！");
                }
            } catch (SQLException e) {
                throw new RuntimeException("关闭Statement出现异常:" + e.getMessage());
            } finally {
                if (null != conn) {
                    try {
                        conn.close();
                        System.out.println("Connection已关闭！");
                    } catch (SQLException e) {
                        throw new RuntimeException("关闭Connection出现异常:"
                                + e.getMessage());
                    }
                }
            }
        }

    }
}

接着在使用JDBC的地方，调用free（），如下：

原文出处：http://blog.csdn.net/xuan6251237011/article/details/12089311

懒汉式

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DatabaseConnection {
    private static final String DBDRIVER = "org.gjt.mm.mysql.Driver";
    private static final String DBURL = "jdbc:mysql://localhost:3306/test";
    private static final String DBUSER = "root";
    private static final String PASSWORD = "admin";
    private Connection conn = null;

    // 如果要实例化本类对象，实际上就是为了取得数据库连接，那么就把连接过程交给构造方法
    public DatabaseConnection() {
        try {
            Class.forName(DBDRIVER);
            this.conn = DriverManager.getConnection(DBURL, DBUSER, DBPASSWORD);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public Connection getConnection() {
        return this.conn;
    }

    public void close() {
        if (this.conn != null) {
            try { // 关闭时几乎不会有问题
                this.conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

饿汉式

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DataBaseConnection {
    private static final String DBDRIVER = "org.gjt.mm.mysql.Driver";
    private static final String DBURL = "jdbc:mysql://localhost:3306/test";
    private static final String DBUSER = "root";
    private static final String PASSWORD = "admin";
    public Connection conn;

    //饿汉式数据库连接
    public Connection getConnection() {
        try {
            if (conn == null && conn.isClosed())
                Class.forName(DBDRIVER);
            conn = DriverManager.getConnection(DBURL, DBUSER, PASSWORD);
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return conn;
    }
    public void close(){
        if(conn != null){
            try {
                this.conn.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}