求助！数据库Connection close一次 ，下次再连接就打不开了

[一碗单炒饭]

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
错误是这样的，如果我不对Connection进行关闭，则不会出错，而如果我加了conn.close();之后，下一次再进来这边就会报错
大家帮帮我

/**
	 * 获取按钮事件
	 * 
	 * @return
	 * @throws SQLException
	 */
	public List<AlarmData> getNewButtonStat2() throws SQLException {
		List<AlarmData> list = new ArrayList<AlarmData>();
		Connection conn = MySQLDBUtil.getConn();
		
		Statement statement = conn.createStatement();
		// 通过查询返回结果
		ResultSet rs = statement
				.executeQuery("SELECT  id,bid,keyid,ttime,yn,status FROM(SELECT * FROM t_alarmdata WHERE bid BETWEEN 9 AND 12 ORDER BY ttime DESC LIMIT 2000) a GROUP BY a.bid,a.keyid");
		// 循环取出 rs 中的结果
		while (rs.next()) {
			AlarmData ad = new AlarmData();
			ad.setBid(rs.getString("bid"));
			ad.setId(rs.getInt("id"));
			ad.setKeyid(rs.getString("keyid"));
			ad.setStatus(rs.getInt("status"));
			ad.setYn(rs.getInt("yn"));
			list.add(ad);
		}
		rs.close();
		statement.close();
		conn.close(); // 如果这里的不关闭，则没有错误信息，加上conn.close(); 下次再进来这里就会报如下错误
		System.out.println(list.size());
		return list;
	}

MySQLDBUtil 数据库链接类

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

public class MySQLDBUtil {
	
	// 本机
	private static final String URL = "jdbc:mysql://127.0.0.1:3306/warning_light";
	
	private static final String USER = "root";
	
	private static final String PASSWORD = "888888";
	
	private static Connection conn = null;
	
	DBPool dbp = null;

	static {
		// 1.加载驱动（反射机制）
				try {
					Class.forName("com.mysql.jdbc.Driver");
					// 2.获得数据库连接
					conn = DriverManager.getConnection(URL, USER, PASSWORD);
				} catch (ClassNotFoundException e) {
					System.out.println("sorry,can't find the Driver!");
					e.printStackTrace();
				} catch (SQLException e) {
					System.out.println(conn);
					e.printStackTrace();
				}
	}
	
	public MySQLDBUtil(){
		
	}
	
	public static Connection getConn() {
		return conn;
	}

}

错误信息

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
	at java.lang.reflect.Constructor.newInstance(Unknown Source)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
	at com.mysql.jdbc.Util.getInstance(Util.java:381)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:984)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)
	at com.mysql.jdbc.ConnectionImpl.checkClosed(ConnectionImpl.java:1098)
	at com.mysql.jdbc.ConnectionImpl.createStatement(ConnectionImpl.java:2380)
	at com.mysql.jdbc.ConnectionImpl.createStatement(ConnectionImpl.java:2362)
// 第一段代码的11行
	at com.lewei.dao.WarningLightDao.getNewButtonStat2(WarningLightDao.java:137)// 第一段代码的11行
	at com.lewei.www.WarningScreen$6.doInBackground(WarningScreen.java:983)
	at com.lewei.www.WarningScreen$6.doInBackground(WarningScreen.java:1)
	at javax.swing.SwingWorker$1.call(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at javax.swing.SwingWorker.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)

[soton_dolphin]

public static Connection getConn() {
   if (conn == null){
    // get connection
 }
        return conn;
    }

[一碗单炒饭]

引用 1 楼 soton_dolphin 的回复:

public static Connection getConn() {
   if (conn == null){
    // get connection
 }
        return conn;
    }

public static Connection getConn() {
		if(conn == null){
			try {
				Class.forName("com.mysql.jdbc.Driver");
				conn = DriverManager.getConnection(URL, USER, PASSWORD);
			} catch (SQLException | ClassNotFoundException e) {
				e.printStackTrace();
			}
		}
		return conn;
	}

是这样吗？不行呢

[soton_dolphin]

楼主在这段代码上加上TRY CATCH， 看看是哪里抛出来的异常

[soton_dolphin]

刚刚看到你的connection是static的。不可以把connection 定义为static, 只能是成员变量

[淼哥]

引用 4 楼 soton_dolphin 的回复:

刚刚看到你的connection是static的。不可以把connection 定义为static, 只能是成员变量

+1

[一碗单炒饭]

引用 4 楼 soton_dolphin的回复:

刚刚看到你的connection是static的。不可以把connection 定义为static, 只能是成员变量

好的，谢谢，今天搬家，明天测试一下。

[拾叁L]

static { // 1.加载驱动（反射机制） try { Class.forName("com.mysql.jdbc.Driver"); // 2.获得数据库连接 conn = DriverManager.getConnection(URL, USER, PASSWORD); } catch (ClassNotFoundException e) { System.out.println("sorry,can't find the Driver!"); e.printStackTrace(); } catch (SQLException e) { System.out.println(conn); e.printStackTrace(); } } 你这里面的静态代码块只会在MySQLDBUtil类第一次调用的时候被执行，也就是说conn只在你第一次调用Connection conn = MySQLDBUtil.getConn();时候得到连接，你把它close了就不会再执行conn = DriverManager.getConnection(URL, USER, PASSWORD);获取连接了

[一碗单炒饭]

引用 7 楼 ll8128的回复:

static { // 1.加载驱动（反射机制） try { Class.forName("com.mysql.jdbc.Driver"); // 2.获得数据库连接 conn = DriverManager.getConnection(URL, USER, PASSWORD); } catch (ClassNotFoundException e) { System.out.println("sorry,can't find the Driver!"); e.printStackTrace(); } catch (SQLException e) { System.out.println(conn); e.printStackTrace(); } } 你这里面的静态代码块只会在MySQLDBUtil类第一次调用的时候被执行，也就是说conn只在你第一次调用Connection conn = MySQLDBUtil.getConn();时候得到连接，你把它close了就不会再执行conn = DriverManager.getConnection(URL, USER, PASSWORD);获取连接了

好的，谢谢你(^_^)

[一碗单炒饭]

问题解决了，谢谢 @soton_dolphin @ll8128