每个脚本引擎实例都具有一个默认的上下文，在其中，可以用put方法存储变量，而所执行的脚本的输出则被默认定向到System . out。

Each script-engine instance has a default context where you can store variables with the put method and the output of any executed script is directed to System.out by default.

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然后，设置另一个会话变量（更新消息），并将用户重定向回 index.php 页面。

Then another session variable is set (the update message), and the user is redirected back to the index.php page.

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