Java 捕获JDBC类中的未知hostException

我使用JDBC和c3p0将Swing应用程序连接到PostgreSQL数据库。当连接断开时，它会不可控地引发几个PSQLException和UnknownHostException，这是预期的

ago 17, 2017 5:39:25 PM org.postgresql.Driver connect
GRAVE: Connection error: 
org.postgresql.util.PSQLException: El intento de conexión falló.
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:275)
    at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:49)
    at org.postgresql.jdbc.PgConnection.<init>(PgConnection.java:194)
    at org.postgresql.Driver.makeConnection(Driver.java:450)
    at org.postgresql.Driver.connect(Driver.java:252)
    at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:175)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125)
    at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
    at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870)
    at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)
Caused by: java.net.UnknownHostException: academico.ulasalle.edu.pe
    at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
    at java.net.PlainSocketImpl.connect(Unknown Source)
    at java.net.SocksSocketImpl.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at org.postgresql.core.PGStream.<init>(PGStream.java:68)
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:144)
    ... 13 more

---

马上澄清一下：

UnknownHostException

不是直接抛出的，而是（可能间接地）封装在一些

SQLException

中

我想你会发现包装异常

} catch (final SQLException e) {
    e.printStackTrace();
} finally {

在

RS\u Query（）

方法中

一种策略是捕获异常包装

UnknownHostException

，将其包装在自定义运行时异常中，并允许它飞到UI，在那里您可以捕获它并显示错误窗口（或非阻塞弹出窗口）

其中

RuntimeUnknownHostException

扩展

RuntimeException

然后在全局UI异常处理程序中处理它：

try {
    // some code calling conn.RS_Query(...);
} catch (RuntimeUnknownHostException e) {
    ... display the error message
}

检测代码：

private boolean causedByUnknownHostException(Throwable t) {
    if (t == null) {
        return false;
    }
    if (t instanceof UnknownHostException) {
        return true;
    }
    return causedByUnknownHostException(t.getCause());
}

---

为什么要取消选中异常（扩展

RuntimeException

）？这将避免在所有中间方法中声明它的负担，因此它可以到达您的集中化UI异常处理程序。

您好，在查看具体问题之前，这个类有很多问题。每次查询后，您都会关闭（）连接池，这不是很好。连接池应该是长寿命的；在查询结束时，只应关闭连接。应该在finally块中关闭的是连接，而不是连接池（或者更好的方法是，将连接用作资源。非常感谢，我正在更改它。我尝试了它，但没有在那里捕获异常。此外，当我尝试在那里捕获UnknownHostException时，该块被指示为无法访问，因为该异常从未从“try”块中抛出。很抱歉，我错了，当然是

UnknownHostEx异常

不扩展

SQLException

，但在您的情况下，它由

SQLException

的子类包装。根据此更新了答案。

try {
    // some code calling conn.RS_Query(...);
} catch (RuntimeUnknownHostException e) {
    ... display the error message
}

private boolean causedByUnknownHostException(Throwable t) {
    if (t == null) {
        return false;
    }
    if (t instanceof UnknownHostException) {
        return true;
    }
    return causedByUnknownHostException(t.getCause());
}