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Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class Properties - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.util
Class Properties

java.lang.Object
  |
  +--java.util.Dictionary
        |
        +--java.util.Hashtable
              |
              +--java.util.Properties

Direct Known Subclasses:

Provider

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public class Properties

extends Hashtable

The Properties class represents a persistent set of properties. The Properties can be saved to a stream or loaded from a stream. Each key and its corresponding value in the property list is a string.

A property list can contain another property list as its "defaults"; this second property list is searched if the property key is not found in the original property list. Because Properties inherits from Hashtable, the put and putAll methods can be applied to a Properties object. Their use is strongly discouraged as they allow the caller to insert entries whose keys or values are not Strings. The setProperty method should be used instead. If the store or save method is called on a "compromised" Properties object that contains a non-String key or value, the call will fail.

Since:

JDK1.0

See Also:

Serialized Form

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Field Summary
protected  Properties	defaults           A property list that contains default values for any keys not found in this property list.

 

Constructor Summary

Properties()           Creates an empty property list with no default values.

Properties(Properties defaults)           Creates an empty property list with the specified defaults.

 

Method Summary
String	getProperty(String key)           Searches for the property with the specified key in this property list.
String	getProperty(String key, String defaultValue)           Searches for the property with the specified key in this property list.
void	list(PrintStream out)           Prints this property list out to the specified output stream.
void	list(PrintWriter out)           Prints this property list out to the specified output stream.
void	load(InputStream inStream)           Reads a property list (key and element pairs) from the input stream.
Enumeration	propertyNames()           Returns an enumeration of all the keys in this property list, including the keys in the default property list.
void	save(OutputStream out, String header)           Deprecated. This method does not throw an IOException if an I/O error occurs while saving the property list. As of JDK 1.2, the preferred way to save a properties list is via the store(OutputStream out, String header) method.
Object	setProperty(String key, String value)           Calls the hashtable method put.
void	store(OutputStream out, String header)           Writes this property list (key and element pairs) in this Properties table to the output stream in a format suitable for loading into a Properties table using the load method.

 

Methods inherited from class java.util.Hashtable

clear, clone, contains, containsKey, containsValue, elements, entrySet, equals, get, hashCode, isEmpty, keys, keySet, put, putAll, rehash, remove, size, toString, values

 

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

 

Field Detail

defaults

protected Properties defaults

A property list that contains default values for any keys not found in this property list.

Constructor Detail

Properties

public Properties()

Creates an empty property list with no default values.

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Properties

public Properties(Properties defaults)

Creates an empty property list with the specified defaults.

Parameters:

defaults - the defaults.

Method Detail

setProperty

public Object setProperty(String key,
                          String value)

Calls the hashtable method put. Provided for parallelism with the getProperties method. Enforces use of strings for property keys and values.

Since:

JDK1.2

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load

public void load(InputStream inStream)
          throws IOException

Reads a property list (key and element pairs) from the input stream.

Every property occupies one line of the input stream. Each line is terminated by a line terminator (\n or \r or \r\n). Lines from the input stream are processed until end of file is reached on the input stream.

A line that contains only whitespace or whose first non-whitespace character is an ASCII # or ! is ignored (thus, # or ! indicate comment lines).

Every line other than a blank line or a comment line describes one property to be added to the table (except that if a line ends with \, then the following line, if it exists, is treated as a continuation line, as described below). The key consists of all the characters in the line starting with the first non-whitespace character and up to, but not including, the first ASCII =, :, or whitespace character. All of the key termination characters may be included in the key by preceding them with a \. Any whitespace after the key is skipped; if the first non-whitespace character after the key is = or :, then it is ignored and any whitespace characters after it are also skipped. All remaining characters on the line become part of the associated element string. Within the element string, the ASCII escape sequences \t, \n, \r, \\, \", \', \ (a backslash and a space), and \\uxxxx are recognized and converted to single characters. Moreover, if the last character on the line is \, then the next line is treated as a continuation of the current line; the \ and line terminator are simply discarded, and any leading whitespace characters on the continuation line are also discarded and are not part of the element string.

As an example, each of the following four lines specifies the key "Truth" and the associated element value "Beauty":

 Truth = Beauty
	Truth:Beauty
 Truth			:Beauty
 

As another example, the following three lines specify a single property:

 fruits				apple, banana, pear, \
                                  cantaloupe, watermelon, \
                                  kiwi, mango
 

The key is "fruits" and the associated element is:

"apple, banana, pear, cantaloupe, watermelon,kiwi, mango"

Note that a space appears before each \ so that a space will appear after each comma in the final result; the \, line terminator, and leading whitespace on the continuation line are merely discarded and are not replaced by one or more other characters.

As a third example, the line:

cheeses
 

specifies that the key is "cheeses" and the associated element is the empty string.

Parameters:

in - the input stream.

Throws:

IOException - if an error occurred when reading from the input stream.

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save

public void save(OutputStream out,
                 String header)

Deprecated. This method does not throw an IOException if an I/O error occurs while saving the property list. As of JDK 1.2, the preferred way to save a properties list is via the store(OutputStream out, String header) method.

Calls the store(OutputStream out, String header) method and suppresses IOExceptions that were thrown.

Parameters:

out - an output stream.

header - a description of the property list.

Throws:

ClassCastException - if this Properties object contains any keys or values that are not Strings.

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store

public void store(OutputStream out,
                  String header)
           throws IOException

Writes this property list (key and element pairs) in this Properties table to the output stream in a format suitable for loading into a Properties table using the load method.

Properties from the defaults table of this Properties table (if any) are not written out by this method.

If the header argument is not null, then an ASCII # character, the header string, and a line separator are first written to the output stream. Thus, the header can serve as an identifying comment.

Next, a comment line is always written, consisting of an ASCII # character, the current date and time (as if produced by the toString method of Date for the current time), and a line separator as generated by the Writer.

Then every entry in this Properties table is written out, one per line. For each entry the key string is written, then an ASCII =, then the associated element string. Each character of the element string is examined to see whether it should be rendered as an escape sequence. The ASCII characters \, tab, newline, and carriage return are written as \\, \t, \n, and \r, respectively. Characters less than and characters greater than ~ are written as \\uxxxx for the appropriate hexadecimal value xxxx. Space characters, but not embedded or trailing space characters, are written with a preceding \. The key and value characters #, !, =, and : are written with a preceding slash to ensure that they are properly loaded.

After the entries have been written, the output stream is flushed. The output stream remains open after this method returns.

Parameters:

out - an output stream.

header - a description of the property list.

Throws:

ClassCastException - if this Properties object contains any keys or values that are not Strings.

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getProperty

public String getProperty(String key)

Searches for the property with the specified key in this property list. If the key is not found in this property list, the default property list, and its defaults, recursively, are then checked. The method returns null if the property is not found.

Parameters:

key - the property key.

Returns:

the value in this property list with the specified key value.

See Also:

defaults

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getProperty

public String getProperty(String key,
                          String defaultValue)

Searches for the property with the specified key in this property list. If the key is not found in this property list, the default property list, and its defaults, recursively, are then checked. The method returns the default value argument if the property is not found.

Parameters:

key - the hashtable key.

defaultValue - a default value.

Returns:

the value in this property list with the specified key value.

See Also:

defaults

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propertyNames

public Enumeration propertyNames()

Returns an enumeration of all the keys in this property list, including the keys in the default property list.

Returns:

an enumeration of all the keys in this property list, including the keys in the default property list.

See Also:

Enumeration, defaults

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list

public void list(PrintStream out)

Prints this property list out to the specified output stream. This method is useful for debugging.

Parameters:

out - an output stream.

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list

public void list(PrintWriter out)

Prints this property list out to the specified output stream. This method is useful for debugging.

Parameters:

out - an output stream.

Since:

JDK1.1

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