In block 1, the servlet checks for a session object by invoking a method on the request object, res, which was passed to the servlet method as a parameter.
在block1中，servlet通过调用请求对象、res(作为参数被传递到servlet方法)的方法检查session对象。
Number of blocks and total block time: the number of instances and total elapsed time when the thread was in a BLOCKED state while invoking a method or service.
阻塞数量和总阻塞时间：在调用某个方法或服务时，处于BLOCKED状态的线程的实例数量和总占用时间。
When invoking unknown code (which listeners certainly qualify as), it is prudent to execute it in a try-catch block so that ill-behaved listeners do not do more damage than necessary.
在调用未知代码(侦听器就是这样的代码)时，谨慎的方式是在try - catch块中执行它，这样，行为有误的侦听器不会造成更多不必要的破坏。
When invoking unknown code (which listeners certainly qualify as), it is prudent to execute it in a try-catch block so that ill-behaved listeners do not do more damage than necessary.
在调用未知代码(侦听器就是这样的代码)时，谨慎的方式是在try - catch块中执行它，这样，行为有误的侦听器不会造成更多不必要的破坏。
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