ch.agent.core

Class KeyedMessage

java.lang.Object

ch.agent.core.KeyedMessage

Direct Known Subclasses:

T2Msg

public abstract class KeyedMessage
extends Object

A keyed message is a text identified by a key unique within a category. The text is obtained from a MessageBundle. Such a message can be easily identified in a large system with thousands of messages. In large systems, messages are grouped in categories with corresponding textual resources. Within each category, each message has a unique key. The messages themselves contain parameters following the MessageFormat convention.

Messages are only prepared when fetched with getMessage(). Preparation involves looking up messages in a resource bundle and formatting parameters. Avoiding this overhead is especially useful when messages are sent to a logging facility without knowing for sure that they will actually be logged. Thanks to this feature, it is not necessary to bracket the logging calls with tests of the current logging level. To force preparation of the message, for example because objects passed as parameter are about to change, use getMessage(), which makes a copy of the formatted string the first time it is called, and returns the copy on subsequent calls.

An application would extend this class as follows:

public class FOOMsg extends KeyedMessage { public class M { public static final String A123 = "A123"; public static final String X124 = "X124"; } private static final MessageBundle BUNDLE = new MessageBundle("FOO", ResourceBundle.getBundle("ch.agent.foo.FOOMsg")); public static KeyedMessage exception(String code, Object... arg) { return new KeyedMessage(new FOOMsg(code, arg)); } public static KeyedMessage exception(Throwable cause, String code, Object... arg) { return new KeyedMessage(new FOOMsg(code, arg), cause); } public FOOMsg(String code, Object... args) { super(code, BUNDLE, args); } }

The property file ch/agent/foo/FOOMsg.properties would contains lines like:

A123=The answer is {0}. X124=What is the question?

Clients would throw exceptions and write messages so:

System.error.println(new FOOMsg(M.X124)); throw FOOMsg.exception(M.A123, 42);

The user would see:

FOO.X124 - What is the question? FOO.A123 - The answer is 42.

Author:

Jean-Paul Vetterli

Constructor Summary

Constructors

Constructor and Description
KeyedMessage(String key, MessageBundle bundle, Object... args) Construct a keyed message.

Method Summary

Modifier and Type	Method and Description
String	getCategory() Return the message category.
String	getKey() Return the message key.
String	getMessage() Return the formatted text of the message.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

KeyedMessage

public KeyedMessage(String key,
                    MessageBundle bundle,
                    Object... args)

Construct a keyed message. The description is fetched from the message bundle using the key. When one or more arguments are specified, these are inserted into the text. When an argument is null, the string null is inserted, else the method toString() is applied to the argument before it is inserted. Refer to MessageFormat for details on the format of arguments.

Parameters:

key - a String identifying the text

bundle - a MessageBundle containing the wanted text

args - zero of more arguments

Method Detail

getCategory

public String getCategory()

Return the message category. The category, typically a short string, is supplied by the message's MessageBundle.

Returns:

the category

getKey

public String getKey()

Return the message key.

Returns:

the key

getMessage

public String getMessage()

Return the formatted text of the message.

Returns:

the message text

toString

public String toString()

Overrides:

toString in class Object