Java 具有自动重新连接的 JDBC 连接
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JDBC connection with auto reconnect
提问by bumperbox
I am using JDBC to connect to a database server. The connection is over a wireless network and can be dodgy at times. At the moment when the connection is lost I need to close and restart the application.
我正在使用 JDBC 连接到数据库服务器。连接是通过无线网络进行的,有时可能会很棘手。在连接丢失的那一刻,我需要关闭并重新启动应用程序。
Does anyone have some examples of code where I could write some sort of wrapper to automatically reconnect and rerun the last query? This would save a lot of hassles.
有没有人有一些代码示例,我可以在其中编写某种包装器来自动重新连接并重新运行最后一个查询?这样会省去很多麻烦。
I am just not sure how it should/could be implemented. Maybe there is already something available?
我只是不确定它应该/如何实施。也许已经有可用的东西?
采纳答案by Pascal Thivent
Let a connection pool handle this for you, many of them can validate a connection. So does DBCPwhich has a testOnBorrow
parameter that forces a sanity check on every connection before it's used. The default value of this parameter is true
, it just needs validationQuery
to be set to a non-null string to have any effect. So set the validationQuery
and there you go! Check out the documentation.
让连接池为您处理这个问题,其中许多可以验证连接。DBCP也是如此,它有一个testOnBorrow
参数,在使用之前强制对每个连接进行健全性检查。此参数的默认值为true
,只需validationQuery
将其设置为非空字符串即可生效。所以设置validationQuery
然后你去!查看文档。
回答by Gandalf
Check out Oracle's Universal Connection Pool (UCP) libraries. They are fully JDBC 4.0 compliant and implement the isValid()
call to check if a connection is live. It's easy to do this check, if false reconnect, then run your query.
查看 Oracle 的通用连接池 (UCP) 库。它们完全符合 JDBC 4.0 并实现isValid()
调用以检查连接是否有效。执行此检查很容易,如果错误重新连接,则运行您的查询。
While I know you didn't ask about connection pools, you should probably be using one anyway so this will help you twofold.
虽然我知道您没有询问连接池,但无论如何您都应该使用连接池,因此这对您有双重帮助。
回答by zkarthik
Even if you use JDBC connection pool either application server provided or apache commons pooling, it is worthwhile to code a retry logic. Based on the configuration of your application server, the app server would purge all the pooled connections and recreate a fresh set of connections. Here is a sample:
即使您使用应用程序服务器提供的 JDBC 连接池或 apache 公共池,也值得编写重试逻辑。根据应用程序服务器的配置,应用程序服务器将清除所有池连接并重新创建一组新连接。这是一个示例:
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
//
// How many times do you want to retry the transaction
// (or at least _getting_ a connection)?
//
int retryCount = 5;
boolean transactionCompleted = false;
do {
try {
conn = getConnection(); // assume getting this from a
// javax.sql.DataSource, or the
// java.sql.DriverManager
retryCount = 0;
stmt = conn.createStatement();
String query = "Some sample SQL";
rs = stmt.executeQuery(query);
while (rs.next()) {
}
rs.close();
rs = null;
stmt.close();
stmt = null;
conn.close();
conn = null;
transactionCompleted = true;
} catch (SQLException sqlEx) {
//
// The two SQL states that are 'retry-able'
// for a communications error.
//
// Only retry if the error was due to a stale connection,
// communications problem
//
String sqlState = sqlEx.getSQLState();
if ("Substitute with Your DB documented sqlstate number for stale connection".equals(sqlState) ) {
retryCount--;
} else {
retryCount = 0;
}
} finally {
if (rs != null) {
try {
rs.close();
} catch (SQLException sqlEx) {
// log this
}
}
if (stmt != null) {
try {
stmt.close();
} catch (SQLException sqlEx) {
// log this
}
}
if (conn != null) {
try {
//
// If we got here, and conn is not null, the
// transaction should be rolled back, as not
// all work has been done
try {
conn.rollback();
} finally {
conn.close();
}
} catch (SQLException sqlEx) {
//
// If we got an exception here, something
// pretty serious is going on, so we better
// pass it up the stack, rather than just
// logging it. . .
throw sqlEx;
}
}
}
} while (!transactionCompleted && (retryCount > 0));