API java : Properties

java.util
Class Properties

java.lang.Object
  java.util.Dictionary<K,V>
      java.util.Hashtable<Object,Object>
          java.util.Properties

All Implemented Interfaces:

Serializable, Cloneable, Map<Object,Object>

Direct Known Subclasses:

Provider

public class Properties
extends Hashtable<Object,Object>

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.

The load and store methods load and store properties in a simple line-oriented format specified below. This format uses the ISO 8859-1 character encoding. Characters that cannot be directly represented in this encoding can be written using Unicode escapes ; only a single 'u' character is allowed in an escape sequence. The native2ascii tool can be used to convert property files to and from other character encodings.

The loadFromXML(InputStream) and storeToXML(OutputStream, String, String) methods load and store properties in a simple XML format. By default the UTF-8 character encoding is used, however a specific encoding may be specified if required. An XML properties document has the following DOCTYPE declaration:

<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">

<?xml version="1.0" encoding="UTF-8"?>
 
    <!-- DTD for properties -->
 
    <!ELEMENT properties ( comment?, entry* ) >
 
    <!ATTLIST properties version CDATA #FIXED "1.0">
 
    <!ELEMENT comment (#PCDATA) >
 
    <!ELEMENT entry (#PCDATA) >
 
    <!ATTLIST entry key CDATA #REQUIRED>

Since:

JDK1.0

See Also:

native2ascii tool for Solaris, native2ascii tool for Windows, Serialized Form

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.
void	loadFromXML(InputStream in)           Loads all of the properties represented by the XML document on the specified input stream into this properties table.
Enumeration<?>	propertyNames()           Returns an enumeration of all the keys in this property list, including distinct keys in the default property list if a key of the same name has not already been found from the main properties list.
void	save(OutputStream out, String comments)           Deprecated. This method does not throw an IOException if an I/O error occurs while saving the property list. The preferred way to save a properties list is via the store(OutputStream out, String comments) method or the storeToXML(OutputStream os, String comment) method.
Object	setProperty(String key, String value)           Calls the Hashtable method put.
void	store(OutputStream out, String comments)           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.
void	storeToXML(OutputStream os, String comment)           Emits an XML document representing all of the properties contained in this table.
void	storeToXML(OutputStream os, String comment, String encoding)           Emits an XML document representing all of the properties contained in this table, using the specified encoding.

 

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.

Properties

public Properties()

Creates an empty property list with no default values.

Properties

public Properties(Properties defaults)

Creates an empty property list with the specified defaults.

Parameters:

defaults - the defaults.

setProperty

public Object setProperty(String key,
                          String value)

Calls the Hashtable method put. Provided for parallelism with the getProperty method. Enforces use of strings for property keys and values. The value returned is the result of the Hashtable call to put.

Parameters:

key - the key to be placed into this property list.

value - the value corresponding to key.

Returns:

the previous value of the specified key in this property list, or null if it did not have one.

Since:

1.2

See Also:

getProperty(java.lang.String)

load

public void load(InputStream inStream)
          throws IOException

Reads a property list (key and element pairs) from the input stream. The stream is assumed to be using the ISO 8859-1 character encoding; that is each byte is one Latin1 character. Characters not in Latin1, and certain special characters, can be represented in keys and elements using escape sequences similar to those used for character and string literals (see §3.3 and §3.10.6 of the Java Language Specification). The differences from the character escape sequences used for characters and strings are:

• Octal escapes are not recognized.
• The character sequence \b does not represent a backspace character.
• The method does not treat a backslash character, \, before a non-valid escape character as an error; the backslash is silently dropped. For example, in a Java string the sequence "\z" would cause a compile time error. In contrast, this method silently drops the backslash. Therefore, this method treats the two character sequence "\b" as equivalent to the single character 'b'.
• Escapes are not necessary for single and double quotes; however, by the rule above, single and double quote characters preceded by a backslash still yield single and double quote characters, respectively.

An IllegalArgumentException is thrown if a malformed Unicode escape appears in the input.

This method processes input in terms of lines. A natural line of input is terminated either by a set of line terminator characters (\n or \r or \r\n) or by the end of the file. A natural line may be either a blank line, a comment line, or hold some part of a key-element pair. The logical line holding all the data for a key-element pair may be spread out across several adjacent natural lines by escaping the line terminator sequence with a backslash character, \. Note that a comment line cannot be extended in this manner; every natural line that is a comment must have its own comment indicator, as described below. If a logical line is continued over several natural lines, the continuation lines receive further processing, also described below. Lines are read from the input stream until end of file is reached.

A natural line that contains only white space characters is considered blank and is ignored. A comment line has an ASCII '#' or '!' as its first non-white space character; comment lines are also ignored and do not encode key-element information. In addition to line terminators, this method considers the characters space (' ', '\u0020'), tab ('\t', '\u0009'), and form feed ('\f', '\u000C') to be white space.

If a logical line is spread across several natural lines, the backslash escaping the line terminator sequence, the line terminator sequence, and any white space at the start the following line have no affect on the key or element values. The remainder of the discussion of key and element parsing will assume all the characters constituting the key and element appear on a single natural line after line continuation characters have been removed. Note that it is not sufficient to only examine the character preceding a line terminator sequence to see if the line terminator is escaped; there must be an odd number of contiguous backslashes for the line terminator to be escaped. Since the input is processed from left to right, a non-zero even number of 2n contiguous backslashes before a line terminator (or elsewhere) encodes n backslashes after escape processing.

The key contains all of the characters in the line starting with the first non-white space character and up to, but not including, the first unescaped '=', ':', or white space character other than a line terminator. All of these key termination characters may be included in the key by escaping them with a preceding backslash character; for example,

\:\=

would be the two-character key ":=". Line terminator characters can be included using \r and \n escape sequences. Any white space after the key is skipped; if the first non-white space character after the key is '=' or ':', then it is ignored and any white space characters after it are also skipped. All remaining characters on the line become part of the associated element string; if there are no remaining characters, the element is the empty string "". Once the raw character sequences constituting the key and element are identified, escape processing is performed as described above.

As an example, each of the following three 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 white space 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:

inStream - the input stream.

Throws:

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

IllegalArgumentException - if the input stream contains a malformed Unicode escape sequence.

save

@Deprecated
public void save(OutputStream out,
                            String comments)

Deprecated. This method does not throw an IOException if an I/O error occurs while saving the property list. The preferred way to save a properties list is via the store(OutputStream out, String comments) method or the storeToXML(OutputStream os, String comment) method.

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

Parameters:

out - an output stream.

comments - a description of the property list.

Throws:

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

store

public void store(OutputStream out,
                  String comments)
           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. The stream is written using the ISO 8859-1 character encoding.

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

If the comments argument is not null, then an ASCII # character, the comments string, and a line separator are first written to the output stream. Thus, the comments 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 key and element strings is examined to see whether it should be rendered as an escape sequence. The ASCII characters \, tab, form feed, newline, and carriage return are written as \\, \t, \f \n, and \r, respectively. Characters less than \u0020 and characters greater than \u007E are written as \uxxxx for the appropriate hexadecimal value xxxx. For the key, all space characters are written with a preceding \ character. For the element, leading space characters, but not embedded or trailing space characters, are written with a preceding \ character. The key and element characters #, !, =, and : are written with a preceding backslash 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.

comments - a description of the property list.

Throws:

IOException - if writing this property list to the specified output stream throws an IOException.

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

NullPointerException - if out is null.

Since:

1.2

loadFromXML

public void loadFromXML(InputStream in)
                 throws IOException,
                        InvalidPropertiesFormatException

Loads all of the properties represented by the XML document on the specified input stream into this properties table.

The XML document must have the following DOCTYPE declaration:

<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">

Furthermore, the document must satisfy the properties DTD described above.

The specified stream remains open after this method returns.

Parameters:

in - the input stream from which to read the XML document.

Throws:

IOException - if reading from the specified input stream results in an IOException.

InvalidPropertiesFormatException - Data on input stream does not constitute a valid XML document with the mandated document type.

NullPointerException - if in is null.

Since:

1.5

See Also:

storeToXML(OutputStream, String, String)

storeToXML

public void storeToXML(OutputStream os,
                       String comment)
                throws IOException

Emits an XML document representing all of the properties contained in this table.

An invocation of this method of the form props.storeToXML(os, comment) behaves in exactly the same way as the invocation props.storeToXML(os, comment, "UTF-8");.

Parameters:

os - the output stream on which to emit the XML document.

comment - a description of the property list, or null if no comment is desired.

Throws:

IOException - if writing to the specified output stream results in an IOException.

NullPointerException - if os is null.

Since:

1.5

See Also:

loadFromXML(InputStream)

storeToXML

public void storeToXML(OutputStream os,
                       String comment,
                       String encoding)
                throws IOException

Emits an XML document representing all of the properties contained in this table, using the specified encoding.

The XML document will have the following DOCTYPE declaration:

<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">

If the specified comment is null then no comment will be stored in the document.

The specified stream remains open after this method returns.

Parameters:

os - the output stream on which to emit the XML document.

comment - a description of the property list, or null if no comment is desired.

Throws:

IOException - if writing to the specified output stream results in an IOException.

NullPointerException - if os is null, or if encoding is null.

Since:

1.5

See Also:

loadFromXML(InputStream)

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:

setProperty(java.lang.String, java.lang.String), defaults

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:

setProperty(java.lang.String, java.lang.String), defaults

propertyNames

public Enumeration<?> propertyNames()

Returns an enumeration of all the keys in this property list, including distinct keys in the default property list if a key of the same name has not already been found from the main properties list.

Returns:

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

See Also:

Enumeration, defaults

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.

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