![]() The default properties don't need to be saved each time because they never change.įileOutputStream out = new FileOutputStream("appProperties") ĪpplicationProps.store(out, "-No Comment-") The following example writes out the application properties from the previous example using Properties.store. The properties in this file are those that were saved from the application the last time it was invoked, as explained in the next section. If the property can't be found in applicationProps, then its default list is searched.įinally, the code loads a set of properties into applicationProps from a file named appProperties. The defaults come into play when a property is being retrieved. Next, the application uses a different constructor to create a second Properties object, applicationProps, whose default values are contained in defaultProps. Then the load method reads the default values from a file on disk named defaultProperties. This object contains the set of properties to use if values are not explicitly set elsewhere. In = new FileInputStream("appProperties") įirst, the application sets up a default Properties object. Properties applicationProps = new Properties(defaultProps) create application properties with default Properties defaultProps = new Properties() įileInputStream in = new FileInputStream("defaultProperties") The following Java code performs the first two steps described in the previous section: loading the default properties and loading the remembered properties: Upon exiting, the application saves the properties to its well-known location, to be loaded again when the application is next started up. If the users changes are to be remembered in future sessions, they must be saved. The application must always load and save properties to the same location so that it can find them the next time it's executed.ĭuring the execution of the application, the user may change some settings, perhaps in a Preferences window, and the Properties object is updated to reflect these changes. Finally, the application uses the default and remembered properties to initialize itself. Many applications store properties on a per-user basis, so the properties loaded in this step are usually in a specific file in a particular directory maintained by this application in the user's home directory. Next, the application creates another Properties object and loads the properties that were saved from the last time the application was run. class and other resource files for the application. Normally, the default properties are stored in a file on disk along with the. First, the application loads the default properties from a well-known location into a Properties object. The actions given in the first three boxes occur when the application is starting up. The following figure illustrates how a typical application might manage its configuration data with a Properties object over the course of its execution. The remainder of this section explains how to use properties to manage application configuration. For more about these properties, see System Properties. The System class maintains a Properties object that defines the configuration of the current working environment. Java Applets lesson for information about security restrictions on applets. The same code in an applet may not work depending on the browser in which it is running. The example code segments in this section are assumed to be in standalone applications, which, by default, have no security manager. Security Considerations: Access to properties is subject to approval by the current security manager. finding out if the Properties object is empty.enumerating over the values or the keys,.adding a key/value pair to the Properties list,.getting the current number of key/value pairs,.testing to see if a particular key or value is in the Properties object,.Some of the methods inherited from Hashtable support the following actions: loading key/value pairs into a Properties object from a stream,įor an introduction to streams, refer to the section.This class provides methods for the following: To manage properties, create instances of For example, an application capable of downloading files might use a property named "download.lastDirectory" to keep track of the directory used for the last download. The key identifies, and is used to retrieve, the value, much as a variable name is used to retrieve the variable's value. Properties are configuration values managed as key/value pairs.
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