Properties

Properties

java.util

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Java 1.0

cloneable serializable collection

This class is an extension of Hashtable that allows key/value pairs to be read from and written to a stream. The Properties class implements the system properties list, which supports user customization by allowing programs to look up the values of named resources. Because the load( ) and store( ) methods provide an easy way to read and write properties from and to a text stream, this class provides a convenient way to implement an application configuration file.

When you create a Properties object, you may specify another Properties object that contains default values. Keys (property names ) and values are associated in a Properties object with the Hashtable method put( ) . Values are looked up with getProperty( ) ; if this method does not find the key in the current Properties object, it looks in the default Properties object that was passed to the constructor method. A default value can also be specified, in case the key is not found at all. Use setProperty( ) to add a property name /value pair to the Properties object. This Java 1.2 method is preferred over the inherited put( ) method because it enforces the constraint that property names and values be strings.

propertyNames( ) returns an enumeration of all property names (keys) stored in the Properties object and (recursively) all property names stored in the default Properties object associated with it. list( ) prints the properties stored in a Properties object, which can be useful for debugging. store( ) writes a Properties object to a stream, writing one property per line, in name=value format. As of Java 1.2, store( ) is preferred over the deprecated save( ) method, which writes properties in the same way but suppresses any I/O exceptions that may be thrown in the process. The second argument to both store( ) and save( ) is a comment that is written out at the beginning of the property file. Finally, load( ) reads key/value pairs from a stream and stores them in a Properties object. It is suitable for reading both properties written with store( ) and hand-edited properties files. In Java 5.0, storeToXML( ) and loadFromXML( ) are alternatives that write and read properties files using a simple XML grammar.

Figure 16-48. java.util.Properties

 public class  Properties  extends Hashtable<Object,Object> {  // Public Constructors  public  Properties  ( );        public  Properties  (Properties  defaults  );  // Public Instance Methods  public String  getProperty  (String  key  );        public String  getProperty  (String  key  , String  defaultValue  );  1.1  public void  list  (java.io.PrintWriter  out  );        public void  list  (java.io.PrintStream  out  );        public void  load  (java.io.InputStream  inStream  )          throws java.io.IOException;  synchronized   5.0  public void  loadFromXML  (java.io.InputStream  in  )          throws java.io.IOException, InvalidPropertiesFormatException;  synchronized  public Enumeration<?>  propertyNames  ( );  1.2  public Object  setProperty  (String  key  , String  value  );  synchronized   1.2  public void  store  (java.io.OutputStream  out  , String  comments  )          throws java.io.IOException;  synchronized   5.0  public void  storeToXML  (java.io.OutputStream  os  , String  comment  )          throws java.io.IOException;  synchronized   5.0  public void  storeToXML  (java.io.OutputStream  os  , String  comment  , String  encoding  )  throws java.io.IOException;  synchronized   // Protected Instance Fields  protected Properties  defaults  ;  // Deprecated Public Methods   #  public void  save  (java.io.OutputStream  out  , String  comments  );  synchronized  } 

Subclasses

java.security.Provider

Passed To

System.setProperties( ) , javax.xml.transform.Transformer.setOutputProperties( )

Returned By

System.getProperties( ) , javax.xml.transform.Templates.getOutputProperties( ) , javax.xml.transform.Transformer.getOutputProperties( )