Java资源关闭 [英] Java resource closing

问题描述

我正在写一个连接到网站的应用程序，并从中读取一行。我这样做：

  try {
 URLConnection connection = new URL（www.example.com） .openConnection（）; 
 BufferedReader rd = new BufferedReader（new InputStreamReader（connection.getInputStream（）））; 
 String response = rd.readLine（）; 
 rd.close（）; 
} catch（异常e）{
 //异常处理
} 
  

好吗？我的意思是，我关闭了BufferedReader在最后一行，但我不关闭InputStreamReader。应该从connection.getInputStream和独立的InputStreamReader中的BufferedReader创建独立的InputStreamReader，而不是关闭所有这两个读取器？
我认为最好把结束方法放在finally块中，如下所示：

  InputStreamReader isr = null ; 
 BufferedReader br = null; 
 try {
 URLConnection connection = new URL（www.example.com）。openConnection（）; 
 isr = new InputStreamReader（connection.getInputStream（））; 
 br = new BufferedReader（isr）; 
 String response = br.readLine（）; 
} catch（Exception e）{
 //异常处理
} finally {
 br.close（）; 
 isr.close（）; 
} 
  

但它是丑陋的，因为关闭方法可以抛出异常，所以我有处理或抛出它。

哪个解决方案更好？或者什么是最好的解决方案？

解决方案

Java中资源获取和释放的一般成语是：

  final Resource resource = acquire（）; 
 try {
 use（resource）; 
} finally {
 resource.release（）; 
} 
  

注意：

• try 应该立即跟随收购。这意味着你不能将其包装在装饰器中并保持安全（并且移除空格或将东西放在一行上无助于）。


• 每个 ，否则不会是异常安全。


• 避免 null ，使用最终。否则，你会有一些垃圾代码和潜在的NPE。


• 一般来说，除非有更多的资源关联，否则不需要关闭装饰器。但是，您通常需要刷新输出，但在异常情况下可以避免这种情况。


• 异常应该传递给调用者，或者从周围的尝试块（Java引导你误入歧途）

ou可以将这个废话用执行周围的成语，所以你不必重复自己（只写很多的样板）。

I'm writing an app that connect to a website and read one line from it. I do it like this:

try{
        URLConnection connection = new URL("www.example.com").openConnection();
        BufferedReader rd = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String response = rd.readLine();
        rd.close();
    }catch (Exception e) {
        //exception handling
    }

Is it good? I mean, I close the BufferedReader in the last line, but I do not close the InputStreamReader. Should I create a standalone InputStreamReader from the connection.getInputStream, and a BufferedReader from the standalone InputStreamReader, than close all the two readers? I think it will be better to place the closing methods in the finally block like this:

InputStreamReader isr = null;
BufferedReader br = null;
try{
    URLConnection connection = new URL("www.example.com").openConnection();
    isr = new InputStreamReader(connection.getInputStream());
    br = new BufferedReader(isr);
    String response = br.readLine();
}catch (Exception e) {
    //exception handling
}finally{
    br.close();
    isr.close();
}

But it is ugly, because the closing methods can throw exception, so I have to handle or throw it.

Which solution is better? Or what would be the best solution?

解决方案

The general idiom for resource acquisition and release in Java is:

final Resource resource = acquire();
try {
    use(resource);
} finally {
    resource.release();
}

Note:

• try should immediately follow the acquire. This means you can't wrap it in the decorator and maintain safety (and removing spaces or putting things on one line doesn't help:).
• One release per finally, otherwise it wont be exception safe.
• Avoid null, use final. Otherwise you'll have messy code and potential for NPEs.
• Generally there is no need to close the decorator unless it has a further resource associated with it. However, you will generally need to flush outputs, but avoid that in the exception case.
• The exception should either be passed through to the caller, or caught from a surrounding try block (Java leads you astray here).

ou can abstract this nonsense with the Execute Around idiom, so you don't have to repeat yourself (just write a lot of boilerplate).

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