当我尝试在 finally 块中关闭 BufferedReader 时，为什么 eclipse 会抱怨？

Question

这是我的代码：

public static String readFile()
    {

        BufferedReader br = null;
        String line;
        String dump="";

        try
        {
            br = new BufferedReader(new FileReader("dbDumpTest.txt"));
        }
        catch (FileNotFoundException fnfex)
        {
            System.out.println(fnfex.getMessage());
            System.exit(0);
        }

        try
        {
            while( (line = br.readLine()) != null)
            {
                dump += line + "\r\n";
            }
        }
        catch (IOException e)
        {
            System.out.println(e.getMessage() + " Error reading file");
        }
        finally
        {
            br.close();
        }
        return dump;

所以 eclipse 抱怨由 br.close();

引起的未处理的 IO 异常

为什么会导致IO异常？

我的第二个问题是为什么 eclipse 不抱怨以下代码：

InputStream is = null; 
      InputStreamReader isr = null;
      BufferedReader br = null;

      try{
         // open input stream test.txt for reading purpose.
         is = new FileInputStream("c:/test.txt");

         // create new input stream reader
         isr = new InputStreamReader(is);

         // create new buffered reader
         br = new BufferedReader(isr);

         // releases any system resources associated with reader
         br.close();

         // creates error
         br.read();

      }catch(IOException e){

         // IO error
         System.out.println("The buffered reader is closed");
      }finally{

         // releases any system resources associated
         if(is!=null)
            is.close();
         if(isr!=null)
            isr.close();
         if(br!=null)
            br.close();
      }
   }
}

如果您能尽可能用通俗易懂的语言进行解释，我将不胜感激。预先感谢您的帮助

Answer 1

两个代码示例都应该有编译器错误，抱怨未处理的 IOException。 Eclipse 在我的两个代码示例中都将这些显示为错误。

原因是 close 方法在 try 块之外的 finally 块中调用时抛出一个 IOException，一个检查异常。

修复方法是使用 try-with-resources statement，它在 Java 1.7+ 中可用。声明的资源隐式关闭。

try (BufferedReader br = new BufferedReader(new FileReader("dbDumpTest.txt")))
{
   // Your br processing code here
}
catch (IOException e)
{
   // Your handling code here
}
// no finally necessary.

在 Java 1.7 之前，您需要将对 close() 的调用包装在 finally 块内的它们自己的 try-catch 块中。这是很多冗长的代码，以确保关闭和清理所有内容。

finally
{
    try{ if (is != null) is.close(); } catch (IOException ignored) {}
    try{ if (isr != null) isr.close(); } catch (IOException ignored) {}
    try{ if (br != null) br.close(); } catch (IOException ignored) {}
}

当我尝试在 finally 块中关闭 BufferedReader 时，为什么 eclipse 会抱怨？

Why is eclipse complaining when I try to close BufferedReader in finally block?

java

eclipse

exception

bufferedreader

try-catch-finally