3.2.3服务端优化
在阿里“救了八年火”的架构师，大话系统架构优化项目
【案例】记一次资源泄露，具体表现为RESULT-SET未关闭：
在阿里“救了八年火”的架构师，大话系统架构优化项目
RESULT-SET未关闭统计
根据堆栈跟踪日志查看应用程序发现程序代码存在只关闭connection未关闭Statement和ResultSet的问题。
针对关闭connection是否会自动关闭Statement和ResultSet的问题，以及Statement和ResultSet所占用资源是否会自动释放问题，JDBC处理规范或JDK规范中做了如下描述：
JDBC处理规范
JDBC. 3.0 Specification——13.1.3 Closing Statement Objects
An application calls the method Statement.close toindicate that it has finished processing a statement. All Statement objectswill be closed when the connection that created them is closed. However, it isgood coding practice for applications to close statements as soon as they havefinished processing them. This allows any external resources that the statementis using to be released immediately.
Closing a Statement object will close and invalidateany instances of ResultSet produced by that Statement object. The resourcesheld by the ResultSet object may not be released until garbage collection runsagain, so it is a good practice to explicitly close ResultSet objects when theyare no longer needed.
These comments about closing Statement objects applyto PreparedStatement and CallableStatement objects as well.
JDBC. 4.0 Specification——13.1.4 Closing Statement Objects
An application calls the method Statement.close toindicate that it has finished processing a statement. All Statement objectswill be closed when the connection that created them is closed. However, it isgood coding practice for applications to close statements as soon as they havefinished processing them. This allows any external resources that the statementis using to be released immediately.
Closing a Statement object will close and invalidateany instances of ResultSet produced by that Statement object. The resourcesheld by the ResultSet object may not be released until garbage collection runsagain, so it is a good practice to explicitly close ResultSet objects when theyare no longer needed.
Once a Statement has been closed, any attempt toaccess any of its methods with the exception of the isClosed or close methodswill result in a SQLException being thrown.
These comments about closing Statement objects applyto PreparedStatement and CallableStatement objects as well.
规范说明：connection.close 自动关闭 Statement.close 自动导致 ResultSet 对象无效(注意只是 ResultSet 对象无效，ResultSet 所占用的资源可能还没有释放)。所以还是应该显式执行connection、Statement、ResultSet的close方法。特别是在使用connection pool的时候，connection.close 并不会导致物理连接的关闭，不执行ResultSet的close可能会导致更多的资源泄露。
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