Java in a Nutshell, 5th Edition [Electronic resources] نسخه متنی

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(
)