e.getMessage() 和 e.getLocalizedMessage() 之间的区别

Question

What is the difference between the getMessage<\/code><\/a> and getLocalizedMessage<\/code><\/a> methods on Java exceptions?

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Answer 1

As everybody has mentioned above --

To my understanding, getMessage() returns the name of the exception. getLocalizedMessage() returns the name of the exception in the local language of the user (Chinese, Japanese etc.). In order to make this work, the class you are calling getLocalizedMessage() on must have overridden the getLocalizedMessage() method. If it hasn't, the method of one of it's super classes is called which by default just returns the result of getMessage.

In addition to that, I would like to put some code segment explaining how to use it.

How to use it

Java does nothing magical, but it does provide a way to make our life easier. To use getLocalizedMessage() effectively, we have to override the default behavior.

import java.util.ResourceBundle;

public class MyLocalizedThrowable extends Throwable {

    ResourceBundle labels = ResourceBundle.getBundle("loc.exc.test.message");

    private static final long serialVersionUID = 1L;
    public MyLocalizedThrowable(String messageKey) {
        super(messageKey);
    }

    public String getLocalizedMessage() {
        return labels.getString(getMessage());
    }
}

java.util.ResourceBundle is used to do localization.

In this example, you have to place language-specific property files in the loc/exc/test path. For example:

message_fr.properties (containing some key and value):

key1=this is key one in France

message.properties (containing some key and value):

key1=this is key one in English

Now, let us assume that our exception generator class is something like

public class ExceptionGenerator {

    public void generateException() throws MyLocalizedThrowable {
        throw new MyLocalizedThrowable("key1");
    }
}

and the main class is:

public static void main(String[] args) {
    //Locale.setDefault(Locale.FRANCE);
    ExceptionGenerator eg = new ExceptionGenerator();

    try {
        eg.generateException();
    } catch (MyLocalizedThrowable e) {
        System.out.println(e.getLocalizedMessage());
    }
}

By default, it will return the "English" key value if you are executing in the "English" environment. If you set the local to France, you will get the output from the message_fr file.

When to use it

If your application needs to support l10n/i18n you need to use it. But most of the application does not need to, as most error messages are not for the end customer, but for the support engineer/development engineer.

Answer 2

It is really surprising - Check the openJDK 7 code of Throwable.java class.

Implementation of getLocalizedMessage is -

390     public String getLocalizedMessage() {
391         return getMessage();
392     }

And implemenation of getMessage is -

376     public String getMessage() {
377         return detailMessage;
378     }

And

130     private String detailMessage;

There is no change in implemenation of both method but documentation.

Answer 3

no. it definitely does not mean language specific implementations. it means implementations that use an internationalization (aka i18n) mechanism. see this page for more details of what resource bundles are and how to use them.

the gist is that you place any text in resource files, of which you have many (one per locale/language/etc) and your code uses a mechanism to look up the text in the correct resource file (the link i provided goes into details).

as to when and where this gets used, its entirely up to you. normally you'd only be concerned about this when you want to present an exception to a non-technical user, who may not know english that well. so for example, if you're just writing to log (which commonly only technical users read and so isnt a common i18n target) you'd do:

try {
   somethingDangerous();
} catch (Exception e) {
   log.error("got this: "+e.getMessage());
}

but if you intend to display the exception message to the screen (as a small dialogue, for example) then you might want to display the message in a local language:

try {
   somethingDangerous();
} catch (Exception e) {
   JOptionPane.showMessageDialog(frame,
    e.getLocalizedMessage(),
    "Error",  <---- also best be taken from i18n
    JOptionPane.ERROR_MESSAGE);
}

Answer 4

public String  getMessage() 

Returns the detail message string of this throwable.

public String getLocalizedMessage() 

Creates a localized description of this throwable. Subclasses may override this method in order to produce a locale-specific message. For subclasses that do not override this method, the default implementation returns the same result as getMessage() .

In your case e is nothing but the object of exception ...

getLocalizedMessage() u need to override and give your own message ie the meaning for localized message.

For example ... if there is a null pointer exception ...

By printing e it will display null

e.getMessage() ---> NullPointerException

Answer 5

This is what the Throwable.java class have to say. Maybe it can help someone:

/**
 * Returns the detail message string of this throwable.
 *
 * @return  the detail message string of this {@code Throwable} instance
 *          (which may be {@code null}).
 */
public String getMessage() {
    return detailMessage;
}

/**
 * Creates a localized description of this throwable.
 * Subclasses may override this method in order to produce a
 * locale-specific message.  For subclasses that do not override this
 * method, the default implementation returns the same result as
 * {@code getMessage()}.
 *
 * @return  The localized description of this throwable.
 * @since   JDK1.1
 */
public String getLocalizedMessage() {
    return getMessage();
}

Answer 6

The getLocalizedMessage() method of Throwable class is used to get a locale-specific description of the Throwable object when an Exception Occurred. It helps us to modify the description of the Throwable object according to the local Specific message. For the subclasses which do not override this method, the default implementation of this method returns the same result as getMessage() .

Read more here

Answer 7

To my understanding, getMessage returns the name of the exception. getLocalizedMessage returns the name of the exception in the local language of the user (Chinese, Japanese etc.). In order to make this work, the class you are calling getLocalizedMessage on must have overridden the getLocalizedMessage method. If it hasn't, the method of one of it's super classes is called which by default just returns the result of getMessage.

So in most cases, the result will be the same but in some cases it will return the exception name in the language of the region where the program is being run.

Does that mean language specific implementations ? like if i use e.getLocalizedMessage() for example my app in English - error will be thrown in English , if i use my app in Spanish - then error will be thrown in Spanish

public String 
getMessage() 

Returns the detail message string of this throwable.





public String 
getLocalizedMessage() 

Creates a localized description of this throwable. Subclasses may override this method in order to produce a locale-specific message. For subclasses that do not override this method, the default implementation returns the same result as getMessage().

In your case e is nothing but the object of exception ...

getLocalizedMessage() u need to override and give your own message i.e 
the meaning for localized message. 

For example ... if there is a null pointer exception ...

By printing e it will display null

e.getMessage() ---> NullPointerException 

Read more...

Answer 8

To my understanding, getMessage returns the name of the exception.

getLocalizedMessage returns the name of the exception in the local language of the user (Chinese, Japanese etc.).

In order to make this work, the class you are calling getLocalizedMessage on must have overridden the getLocalizedMessage method.

If it hasn't, the method of one of it's super classes is called which by default just returns the result of getMessage .