按照書上的指導配置c3p0，但是執行不成功

一開始執行：

資訊: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, dataSourceName -> 1hgeby99n2wpirj7phm07|69847c5d, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1hgeby99n2wpirj7phm07|69847c5d, idleConnectionTestPeriod -> 

然後我重新整理了十幾次，報如下異常了：

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Data source rejected establishment of connection,  message from server: "Too many connections"

先來看看我配置資料庫連線池的程式碼：

public static Connection getConnection() throws PropertyVetoException, SQLException{//c3p0連線池
		ComboPooledDataSource cpds = new ComboPooledDataSource();
		try {
			cpds.setDriverClass(DriverURL);
		} catch (PropertyVetoException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		cpds.setJdbcUrl(ConURL);
		cpds.setUser(username);
		cpds.setPassword(passwoed);
		cpds.setMaxPoolSize(30);
		cpds.setMinPoolSize(2);
		cpds.setInitialPoolSize(10);
		cpds.setMaxStatements(180);
		return cpds.getConnection();
	}
 

ComboPooledDataSource cpds = new ComboPooledDataSource();

每次getConnection都會建立一個ComboPooledDataSource類，ComboPooledDataSource是重量級類，建立比較耗費資源，當然會報錯

用單例模式來建立ComboPooledDataSource類即可解決問題：

private static ComboPooledDataSource ds;
	static{
		ds = new ComboPooledDataSource();
		try {
			ds.setDriverClass(DriverURL);
		} catch (PropertyVetoException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		ds.setJdbcUrl(ConURL);
		ds.setUser(username);
		ds.setPassword(passwoed);
		ds.setMaxPoolSize(30);
		ds.setMinPoolSize(2);
		ds.setInitialPoolSize(10);
		ds.setMaxStatements(180);
	}
 

public static Connection getConnection() throws PropertyVetoException, SQLException{//用連線池
		return ds.getConnection();
	}