do I need to surround fileInputStream.close with a

问题:

I have the following Java Class that does one thing, fires out values from config.properties.

When it comes time to close the fileInputStream, I think I read on Wikipedia that it is good to have it in a finally block. Because it honestly works just fine in try/catch block.

Can you show me correction to get fileInputStream.close() in a finally section?

ConfigProperties.java package base;

import java.io.FileInputStream;
import java.util.Properties;

public class ConfigProperties {

    public FileInputStream fileInputStream;
    public String property;

    public String getConfigProperties(String strProperty) {

        Properties configProperties = new Properties();
        try {

            fileInputStream = new FileInputStream("resources/config.properties");
            configProperties.load(fileInputStream);
            property = configProperties.getProperty(strProperty);
            System.out.println("getConfigProperties(" + strProperty + ")");

            // use a finally block to close your Stream.
            // If an exception occurs, do you want the application to shut down?

        } catch (Exception ex) {
            // TODO
            System.out.println("Exception: " + ex);
        }
        finally {
            fileInputStream.close();
        }

        return property;
    }
}

Is the solution only to do as Eclipse suggests and do this in the finally block?

finally {
    try {
        fileInputStream.close();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

Thanks everyone!

回答1:

Because FileInputStream.close() throws an IOException, and the finally{} block doesn't catch exceptions. So you need to either catch it or declare it in order to compile. Eclipse's suggestion is fine; catch the IOException inside the finally{} block.

回答2:

Yes, that is the common pre-Java 7 solution. However, with the introduction of Java 7, there are now try-with-resource statements which will automatically close any declared resources when the try block exits:

try (FileInputStream fileIn = ...) {
    // do something
} // fileIn is closed
catch (IOException e) {
    //handle exception
}

回答3:

The standard approach is:

FileInputStream fileInputStream = null;
try {
    fileInputStream = new FileInputStream(...);
    // do something with the inputstream
} catch (IOException e) {
    // handle an exception
} finally { //  finally blocks are guaranteed to be executed
    // close() can throw an IOException too, so we got to wrap that too
    try {
        if (fileInputStream != null) {
            fileInputStream.close();
        }        
    } catch (IOException e) {
        // handle an exception, or often we just ignore it
    }
}