在java中捕获IOException后如何关闭文件？ [英] How do I close a file after catching an IOException in java?

问题描述

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我正在尝试确保使用BufferedReader打开的文件在我捕获IOException时被关闭，但是看起来我的BufferedReader对象是超出范围的catch块。

I am trying to ensure that a file I have open with BufferedReader is closed when I catch an IOException, but it appears as if my BufferedReader object is out of scope in the catch block.

public static ArrayList readFiletoArrayList(String fileName, ArrayList fileArrayList)
{
    fileArrayList.removeAll(fileArrayList);

    try {
        //open the file for reading
        BufferedReader fileIn = new BufferedReader(new FileReader(fileName));

        // add line by line to array list, until end of file is reached
        // when buffered reader returns null (todo). 
        while(true){
                fileArrayList.add(fileIn.readLine());
            }
    }catch(IOException e){
        fileArrayList.removeAll(fileArrayList);
        fileIn.close(); 
        return fileArrayList; //returned empty. Dealt with in calling code. 
    }
}

Netbeans抱怨说找不到符号fileIn catch块，但是我想确保在IOException的情况下，Reader被关闭。如果没有第一次尝试/捕获构造的丑陋，我该怎么做？

Netbeans complains that it "cannot find symbol fileIn" in the catch block, but I want to ensure that in the case of an IOException that the Reader gets closed. How can I do that without the ugliness of a second try/catch construct around the first?

在这种情况下，有关最佳做法的任何提示或指针， p>

Any tips or pointers as to best practise in this situation is appreciated,

推荐答案

 BufferedReader fileIn = null;
 try {
       fileIn = new BufferedReader(new FileReader(filename));
       //etc.
 } catch(IOException e) {
      fileArrayList.removeall(fileArrayList);
 } finally {
     try {
       if (fileIn != null) fileIn.close();
     } catch (IOException io) {
        //log exception here
     }
 }
 return fileArrayList;

有关上述代码的一些事情：

A few things about the above code:

• close应该在一个finally中，否则当代码正常完成时，或者除了IOException之外还会抛出一些其他异常，它不会被关闭。


• 通常，您有一个静态实用程序方法来关闭这样的资源，以便它检查null并捕获任何异常（除了此上下文之外，您不需要执行任何操作）


• 返回属性在尝试之后，所以主线代码和异常捕获都有一个没有冗余的返回方法。


• 如果将return返回到finally中，它将生成一个编译器警告。

• close should be in a finally, otherwise it won't get closed when the code completes normally, or if some other exception is thrown besides IOException.
• Typically you have a static utility method to close a resource like that so that it checks for null and catches any exceptions (which you never want to do anything about other than log in this context).
• The return belongs after the try so that both the main-line code and the exception catching have a return method without redundancy.
• If you put the return inside the finally, it would generate a compiler warning.

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