用Java关闭Reader / Stream [英] Closing Reader/Stream in Java

问题描述

在我的代码中，我必须从控制台读取用户输入：

In my code I have to read user input from console:

class Demo {
    //...some code
    public String readUserInput() throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String userInput = reader.readLine();
        reader.close();
        return userInput;
    }
}

第一次使用方法 readUserInput（）在Demo对象上一切正常。但是当我创建另一个Demo对象并调用方法时 - 它会抛出异常消息

On first time when I use method readUserInput() on Demo object everything is OK. But when I create another Demo object and call method - it throws Exception with the message

Stream closed

"Stream closed"

任何人都可以告诉我，为什么我在不同的不相等的对象上有异常？感谢您的关注。

Can anybody tell me, why I have Exception on different not equal objects? Thank you for your attention.

推荐答案

问题在于：

new InputStreamReader(System.in)

当你关闭你的BufferedReader，它关闭InputStreamReader，后者又关闭System.in。

When you close your BufferedReader, it closes the InputStreamReader, which in turn closes System.in.

这是 合约's .close（） ，其中包含：

This is all (kind of) explained in the contract of Closeable's .close(), which says:

关闭此流并释放与之相关的任何系统资源。

因此，您第二次尝试阅读你的 BufferedReader ，这最终导致数据从 System.in 中读取，但它不可用。因此你的错误。

As a result, the second time you try and read from your BufferedReader, this ultimately results in data being read from System.in, but it is unavailable. Hence your error.

更一般地说，你处理的资源很差。请阅读并学习使用try-with-resources语句。

More generally, you handle your resources poorly. Please read about, and learn to use, the try-with-resources statement.

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