Java 以编程方式检查 JDBC 中的打开连接
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programmatically checking for open connection in JDBC
提问by Chaitanya MSV
How do I check for an open connection in jdbc for oracle database?
如何在 jdbc 中检查 oracle 数据库的打开连接？
Note: conn.isClosed()cannot be used for this.
注意：conn.isClosed()不能用于此。
采纳答案by reallyinsane
Usually a Connection Pool will also use the Connection.isClosed() method to check if the Connection is still valid. The problem is that not all JDBC drivers will handle this call correctly. So I assume that there are some simple check statements just like RealHowTo said. For Oracle he already mentioned the "SELECT 1 FROM Dual" which should succeed always for Oracle databases. I think that there are similar queries for the different database. I can remember that in a previous project we also implemented an own Connection Pool which used such validation queries.
通常连接池也会使用 Connection.isClosed() 方法来检查连接是否仍然有效。问题是并非所有 JDBC 驱动程序都能正确处理此调用。所以我假设有一些简单的检查语句，就像 RealHowTo 所说的那样。对于 Oracle，他已经提到了“SELECT 1 FROM Dual”，它应该总是适用于 Oracle 数据库。我认为对不同的数据库有类似的查询。我记得在之前的一个项目中，我们还实现了一个自己的连接池，它使用了这样的验证查询。
回答by RealHowTo
Something like:
就像是：
Statement stmt = null;
ResultSet rs =null;
try {
stmt = conn.createStatement();
// oracle
rs = stmt.executeQuery("SELECT 1 FROM Dual");
// others
// rs = stmt.executeQuery("SELECT 1");
if (rs.next())
return true; // connection is valid
}
catch (SQLException e) {
// TODO : log the exception ...
return false;
}
finally {
if (stmt != null) stmt.close();
if (rs != null) rs.close();
}
Note that if the connection is coming from a Connection Pool (in a Application Server for example) then the Pool may have a mechanism to check if a connection is valid or not. With BEA, you specify the SELECT in the "test-on-reserve" property.
请注意，如果连接来自连接池（例如在应用程序服务器中），则该池可能具有检查连接是否有效的机制。使用 BEA，您可以在“test-on-reserve”属性中指定 SELECT。
If you are developing your own pool then you may want to take a look at how others are doing it (ex. Proxool).
如果您正在开发自己的池，那么您可能想看看其他人是如何做的（例如Proxool）。
回答by Nicholas
See thisposting.
看到这个帖子。
The referenced solutions are similar to the one posted here (quick query against DUAL to validate) but there is also an interesting solution provided by JBoss specific to Oracle using the proprietary PING method in the Oracle JDBC Connection class. See the code here.
引用的解决方案类似于此处发布的解决方案（针对 DUAL 的快速查询以进行验证），但 JBoss 还使用 Oracle JDBC Connection 类中的专有 PING 方法为 Oracle 提供了一个有趣的解决方案。请参阅此处的代码。
//Nicholas
//尼古拉斯
回答by J?rgen
Use pingDatabase(int timeout)Implemented in OracleConnection since 9.0.1
使用pingDatabase(int timeout)从 9.0.1 开始在 OracleConnection 中实现
