Serializable
, Cloneable
, Map<Object,Object>
Provider
public class Properties extends Hashtable<Object,Object>
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. Similarly, the call to the propertyNames
or list
method will fail if it is called on a "compromised" Properties
object that contains a non-String
key.
The iterators returned by the iterator
method of this class's "collection views" (that is, entrySet()
, keySet()
, and values()
) may not fail-fast (unlike the Hashtable implementation). These iterators are guaranteed to traverse elements as they existed upon construction exactly once, and may (but are not guaranteed to) reflect any modifications subsequent to construction.
The load(Reader)
/
store(Writer, String)
methods load and store properties from and to a character based stream in a simple line-oriented format specified below. The load(InputStream)
/
store(OutputStream, String)
methods work the same way as the load(Reader)/store(Writer, String) pair, except the input/output stream is encoded in ISO 8859-1 character encoding. Characters that cannot be directly represented in this encoding can be written using Unicode escapes as defined in section 3.3 of The Java Language Specification; only a single 'u' character is allowed in an escape sequence.
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. Implementations are required to support UTF-8 and UTF-16 and may support other encodings. An XML properties document has the following DOCTYPE declaration:
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">Note that the system URI (http://java.sun.com/dtd/properties.dtd) is not accessed when exporting or importing properties; it merely serves as a string to uniquely identify the DTD, which is:
<?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>
This class is thread-safe: multiple threads can share a single Properties
object without the need for external synchronization.
Properties
class does not inherit the concept of a load factor from its superclass, Hashtable
.Modifier and Type | Field | Description |
---|---|---|
protected Properties |
defaults |
A property list that contains default values for any keys not found in this property list. |
Constructor | Description |
---|---|
Properties() |
Creates an empty property list with no default values. |
Properties |
Creates an empty property list with no default values, and with an initial size accommodating the specified number of elements without the need to dynamically resize. |
Properties |
Creates an empty property list with the specified defaults. |
Modifier and Type | Method | Description |
---|---|---|
String |
getProperty |
Searches for the property with the specified key in this property list. |
String |
getProperty |
Searches for the property with the specified key in this property list. |
void |
list |
Prints this property list out to the specified output stream. |
void |
list |
Prints this property list out to the specified output stream. |
void |
load |
Reads a property list (key and element pairs) from the input byte stream. |
void |
load |
Reads a property list (key and element pairs) from the input character stream in a simple line-oriented format. |
void |
loadFromXML |
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 |
Deprecated. This method does not throw an IOException if an I/O error occurs while saving the property list. |
Object |
setProperty |
Calls the Hashtable method put . |
void |
store |
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(InputStream) method. |
void |
store |
Writes this property list (key and element pairs) in this Properties table to the output character stream in a format suitable for using the load(Reader) method. |
void |
storeToXML |
Emits an XML document representing all of the properties contained in this table. |
void |
storeToXML |
Emits an XML document representing all of the properties contained in this table, using the specified encoding. |
void |
storeToXML |
Emits an XML document representing all of the properties contained in this table, using the specified encoding. |
Set |
stringPropertyNames() |
Returns an unmodifiable set of keys from this property list where the key and its corresponding value are strings, 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. |
clear, clone, compute, computeIfAbsent, computeIfPresent, contains, containsKey, containsValue, elements, entrySet, equals, get, hashCode, isEmpty, keys, keySet, merge, put, putAll, rehash, remove, size, toString, values
forEach, getOrDefault, putIfAbsent, remove, replace, replace, replaceAll
protected volatile Properties defaults
public Properties()
Properties
object created with this constructor is unspecified.public Properties(int initialCapacity)
initialCapacity
- the Properties
will be sized to accommodate this many elementsIllegalArgumentException
- if the initial capacity is less than zero.public Properties(Properties defaults)
Properties
object created with this constructor is unspecified.defaults
- the defaults.public Object setProperty(String key, String value)
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
.key
- the key to be placed into this property list.value
- the value corresponding to key
.null
if it did not have one.public void load(Reader reader) throws IOException
Properties are processed in terms of lines. There are two kinds of lines, natural lines and logical lines. A natural line is defined as a line of characters that is terminated either by a set of line terminator characters (\n
or \r
or \r\n
) or by the end of the stream. A natural line may be either a blank line, a comment line, or hold all or some of a key-element pair. A logical line holds all the data of a key-element pair, which 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. Lines are read from input until the end of the stream 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-whitespace character; comment lines are also ignored and do not encode key-element information. In addition to line terminators, this format 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 of the following line have no effect on the key or element values. The remainder of the discussion of key and element parsing (when loading) 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 decide 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-whitespace 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-whitespace 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 :BeautyAs another example, the following three lines specify a single property:
fruits apple, banana, pear, \ cantaloupe, watermelon, \ kiwi, mangoThe 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:
cheesesspecifies that the key is
"cheeses"
and the associated element is the empty string ""
. Characters in keys and elements can be represented in escape sequences similar to those used for character and string literals (see sections 3.3 and 3.10.6 of The Java Language Specification). The differences from the character escape sequences and Unicode escapes used for characters and strings are:
\b
does not represent a backspace 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'
. The specified stream remains open after this method returns.
reader
- the input character stream.IOException
- if an error occurred when reading from the input stream.IllegalArgumentException
- if a malformed Unicode escape appears in the input.NullPointerException
- if reader
is null.public void load(InputStream inStream) throws IOException
load(Reader)
and is assumed to use the ISO 8859-1 character encoding; that is each byte is one Latin1 character. Characters not in Latin1, and certain special characters, are represented in keys and elements using Unicode escapes as defined in section 3.3 of The Java Language Specification. The specified stream remains open after this method returns.
inStream
- the input stream.IOException
- if an error occurred when reading from the input stream.IllegalArgumentException
- if the input stream contains a malformed Unicode escape sequence.NullPointerException
- if inStream
is null.@Deprecated public void save(OutputStream out, String comments)
store(OutputStream out,
String comments)
method or the storeToXML(OutputStream os, String comment)
method.store(OutputStream out, String comments)
method and suppresses IOExceptions that were thrown.out
- an output stream.comments
- a description of the property list.ClassCastException
- if this Properties
object contains any keys or values that are not Strings
.public void store(Writer writer, String comments) throws IOException
Properties
table to the output character stream in a format suitable for using the load(Reader)
method. 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. Any one of a line feed (\n
), a carriage return (\r
), or a carriage return followed immediately by a line feed (\r\n
) in comments is replaced by a line separator
and if the next character in comments is not character #
or character !
then an ASCII #
is written out after that line separator.
If the java.properties.date
is set on the command line and is non-empty (as determined by String.isEmpty
), a comment line is written as follows. First, a #
character is written, followed by the contents of the property, followed by a line separator. Any line terminator characters in the value of the system property are treated the same way as noted above for the comments argument. If the system property is not set or is empty, a comment line is written as follows. First, a #
character is written, followed by the current date and time formatted as if by the Date.toString
method, followed by a line separator.
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. 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.
entrySet()
unless entrySet()
is overridden by a subclass to return a different value than super.entrySet()
.writer
- an output character stream writer.comments
- a description of the property list.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 writer
is null.public void store(OutputStream out, String comments) throws IOException
Properties
table to the output stream in a format suitable for loading into a Properties
table using the load(InputStream)
method. Properties from the defaults table of this Properties
table (if any) are not written out by this method.
This method outputs the comments, properties keys and values in the same format as specified in store(Writer)
, with the following differences:
\u
xxxx for their appropriate unicode hexadecimal value xxxx. \u0020
and characters greater than \u007E
in property keys or values are written as \u
xxxx for the appropriate hexadecimal value xxxx. After the entries have been written, the output stream is flushed. The output stream remains open after this method returns.
out
- an output stream.comments
- a description of the property list.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.public void loadFromXML(InputStream in) throws IOException, InvalidPropertiesFormatException
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.
An implementation is required to read XML documents that use the "UTF-8
" or "UTF-16
" encoding. An implementation may support additional encodings.
The specified stream is closed after this method returns.
in
- the input stream from which to read the XML document.IOException
- if reading from the specified input stream results in an IOException
.UnsupportedEncodingException
- if the document's encoding declaration can be read and it specifies an encoding that is not supportedInvalidPropertiesFormatException
- Data on input stream does not constitute a valid XML document with the mandated document type.NullPointerException
- if in
is null.public void storeToXML(OutputStream os, String comment) throws IOException
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");
.
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.IOException
- if writing to the specified output stream results in an IOException
.NullPointerException
- if os
is null.ClassCastException
- if this Properties
object contains any keys or values that are not Strings
.public void storeToXML(OutputStream os, String comment, String encoding) throws IOException
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.
An implementation is required to support writing of XML documents that use the "UTF-8
" or "UTF-16
" encoding. An implementation may support additional encodings.
The specified stream remains open after this method returns.
This method behaves the same as storeToXML(OutputStream os, String comment, Charset charset) except that it will look up the charset using the given encoding name.
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.encoding
- the name of a supported character encoding
IOException
- if writing to the specified output stream results in an IOException
.UnsupportedEncodingException
- if the encoding is not supported by the implementation.NullPointerException
- if os
is null
, or if encoding
is null
.ClassCastException
- if this Properties
object contains any keys or values that are not Strings
.public void storeToXML(OutputStream os, String comment, Charset charset) throws IOException
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.
An implementation is required to support writing of XML documents that use the "UTF-8
" or "UTF-16
" encoding. An implementation may support additional encodings.
Unmappable characters for the specified charset will be encoded as numeric character references.
The specified stream remains open after this method returns.
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.charset
- the charsetIOException
- if writing to the specified output stream results in an IOException
.NullPointerException
- if os
or charset
is null
.ClassCastException
- if this Properties
object contains any keys or values that are not Strings
.public String getProperty(String key)
null
if the property is not found.key
- the property key.public String getProperty(String key, String defaultValue)
key
- the hashtable key.defaultValue
- a default value.public Enumeration<?> propertyNames()
ClassCastException
- if any key in this property list is not a string.public Set<String> stringPropertyNames()
String
are omitted. The returned set is not backed by this Properties
object. Changes to this Properties
object are not reflected in the returned set.
public void list(PrintStream out)
out
- an output stream.ClassCastException
- if any key in this property list is not a string.public void list(PrintWriter out)
out
- an output stream.ClassCastException
- if any key in this property list is not a string.
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/Properties.html