如何在读取属性文件时关闭fileInputStream

Question

I have following code :

    // Read properties file.
     Properties properties = new Properties();
     try {
     properties.load(new FileInputStream("filename.properties"));
     } catch (FileNotFoundException e) {
     system.out.println("FileNotFound");
     }catch (IOException e) {
     system.out.println("IOEXCeption");
     }

Is it required to close the FileInputStream? If yes, how do I do that? I am getting a bad practice error in my code checklist . Asking it to put finally block.

Answer 1

You must the close the FileInputStream , as the Properties instance will not. From the Properties.load() javadoc:

The specified stream remains open after this method returns.

Store the FileInputStream in a separate variable, declared outside of the try and add a finally block that closes the FileInputStream if it was opened:

Properties properties = new Properties();
FileInputStream fis = null;
try {
    fis = new FileInputStream("filename.properties");
    properties.load(fis);
} catch (FileNotFoundException e) {
    system.out.println("FileNotFound");
} catch (IOException e) {
    system.out.println("IOEXCeption");
} finally {
    if (null != fis)
    {
        try
        {
            fis.close();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}

---

Use try-with-resources since Java 7:

final Properties properties = new Properties();
try (final FileInputStream fis =
         new FileInputStream("filename.properties"))
{
    properties.load(fis);
} catch (FileNotFoundException e) {
    system.out.println("FileNotFound");
} catch (IOException e) {
    system.out.println("IOEXCeption");
}

Answer 2

You should always close your streams, and doing it in the finally block is a good practice. The reason for this is that the finally block always gets executed, and you want to make sure that the stream is always closed, even if Something Bad happens.

    FileInputStream inStream = null;
    try {
        inStream = new FileInputStream("filename.properties");
        properties.load(inStream);
    } catch (FileNotFoundException e) {
        System.out.println("FileNotFound");
    } catch (IOException e) {
        System.out.println("IOEXCeption");
    } finally {
        try {
            inStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

If you are using Java 7, this becomes much easier, since a new try-with syntax was introduced. Then you can write like this:

try(FileInputStream inStream = new FileInputStream("filename.properties")){
       properties.load(inStream);
   } catch (FileNotFoundException e) {
        System.out.println("FileNotFound");
   } catch (IOException e) {
        System.out.println("IOEXCeption");
}

and the stream is closed automatically.

Answer 3

here is an example:

    public class PropertiesHelper {
    public static Properties loadFromFile(String file) throws IOException {
        Properties properties = new Properties();
        FileInputStream stream = new FileInputStream(file);
        try {
            properties.load(stream);
        } finally {
            stream.close();
        }
        return properties;
    }
}

Answer 4

You can use Lombok @Cleanup to do it simply. http://projectlombok.org/features/Cleanup.html

 Properties properties = new Properties();
 try {
   @Cleanup FileInputStream myFis = new FileInputStream("filename.properties");
   properties.load(myFis);
 } catch (FileNotFoundException e) {
   System.out.println("FileNotFound");
 }catch (IOException e) {
   System.out.println("IOEXCeption");
 }

Or, only if your are using Java 7, there is the "try with resource" new feature. http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

 Properties properties = new Properties();
 try (FileInputStream myFis = new FileInputStream("filename.properties")) {
   properties.load(myFis);
 } catch (FileNotFoundException e) {
   System.out.println("FileNotFound");
 }catch (IOException e) {
   System.out.println("IOEXCeption");
 }