Java6学习笔记41——JAVA程序的个人设定

1.简介：
以前你想让程序记住用户自定义的习惯，比如界面字体等，你使用一个配置文件，但是在维护多个用户或出现误拼写时还是力不从心。而java.util.prefs包则提供了便利。在线文档写的非常糟糕，将java.util.prefs这个类描述为“a node in a hierarchical collection of preference data”，还说“there are two separate trees of preference nodes, one for user preferences and one for system preferences.”
这个其实没有那么抽象。

2.使用：
创建Preferences对象的方法是使用静态方法userNodeForPackage()。这个方法要求有一个类对象（通过getClass()方法得到）作为它唯一的参数，系统以便确定某个类是驻留在某个包上的，它返回Preferences对象，这个对象可以从那个包中返回用户设定的偏好信息。由于所有程序一般都使用它们自己的包名，这样references对象间就不会冲突了。userNodeForPackage()方法对每个用户返回不同的Preferences对象，因此同一个程序的不同用户也不会冲突。
偏好信息是以键值对的形式存储的，存储偏好设定使用put()方法，取出偏好设定使用get()方法，使用时需要有一个默认值提供。针对int的putInt方法也可以使用。相似的，
* boolean - putBoolean() and getBoolean()
* long - putLong() and getLong()
* float - putFloat() and getFloat()
* double - putDouble() and getDouble())
clear()则清除这个键值对。

3.举例：
import java.util.prefs.*;

/**
* Simple demonstration of the most common usage of the Java
* Preferences API using the user and package based storage
* node. This app uses the user tree to avoid collisions with
* other users and uses the package name, as is conventional,
* to avoid collisions with other applications in other packages.
*
* This is a simple command-line application. It stores only one
* key/value pair, in which key is the string "PrefsValue".
*
* Argument 1 may be either "get", "clear", or "put".
*
* If "get", the value stored under the key "PrefsValue" is
* fetched and displayed.
*
* If "clear", all prefs items for this package are cleared.
*
* If "put", the second command-line argument provides the value
* to be stored. If the second argument is null, a suitable default
* value is used.
*
* If "get" is requested the first time this application is run
* or after a "clear" operation, a suitable default value is
* returned.
*
**/
public class PrefsDemo {
// Define constants for the three possible operations.
private static final int GET = 1;
private static final int CLEAR = 2;
private static final int PUT = 3;

/** Constructs the PrefsDemo application. **/
public PrefsDemo (String[] args) {

// Get the preferences node for this user and this package.
Preferences prefs = Preferences.userNodeForPackage (getClass ());

// Decode the command-line arguments.
String command = null;
String param2 = null;
String param3 = null;
String newvalue = null;
boolean export = false;

System.err.println ("");
if (args.length == 0) {
System.err.println ("No command given, assuming 'get'");
command = "get";
}
else if (args.length == 1) {
command = args[0];
}
else if (args.length == 2) {
command = args[0];
param2 = args[1];
}
else if (args.length == 3) {
command = args[0];
param2 = args[1];
param3 = args[2];
}

// Turn the string commands into ints so they can be used
// in a switch.
int operation;
if (command.equals ("get")) {
operation = GET;
}
else if (command.equals ("clear")) {
operation = CLEAR;
}
else if (command.equals ("put")) {
operation = PUT;
newvalue =
param2!=null ? param2 : "you forgot the value, dummy";
}
else {
System.err.println
("Don't understand command '" + command + "', assuming 'get'");
operation = GET;
}

// See if the 2nd parameter (for GET and CLEAR) or
// 3rd parameter (for PUT) is the string "export".
if (operation == GET || operation == CLEAR) {
export = "export".equalsIgnoreCase (param2);
}
else if (operation == PUT) {
export = "export".equalsIgnoreCase (param3);
}

// Do the operation requested by the command-line argument(s).
switch (operation) {
case CLEAR:
System.err.println ("Clearing preferences");
try {
prefs.clear ();
}
catch (BackingStoreException bse) {
System.err.println (bse);
}
break;
case GET:
String prefs_value = prefs.get ("PrefsValue", "default value");
System.err.println
("Got PrefsValue `" + prefs_value + "' from prefs");
break;
case PUT:
System.err.println ("Putting `" + newvalue + "' into prefs");
prefs.put ("PrefsValue", newvalue);
int num_puts = prefs.getInt ("num_puts", 0);
prefs.putInt ("num_puts", num_puts+1);
System.err.println
("Number of puts since clear is " + (num_puts+1));
break;
} // switch

if (export) {
try {
prefs.exportNode (System.out);
}
catch (java.io.IOException ioe) {
System.err.println (ioe);
}
catch (BackingStoreException bse) {
System.err.println (bse);
}
}

} // ctor

public static void main (String[] args) {
new PrefsDemo (args);
} // main

} // class PrefsDemoApp

下边这篇文字更为详细的介绍了个人偏好设定这个话题：
http://java.sun.com/developer/technicalArticles/releases/preferences/