public classPropertiesextendsHashtable<Object,Object>
Properties class represents a persistent set of properties. TheProperties 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.
BecauseProperties inherits fromHashtable, theput andputAll methods can be applied to aProperties object. Their use is strongly discouraged as they allow the caller to insert entries whose keys or values are notStrings. ThesetProperty method should be used instead. If thestore orsave method is called on a "compromised"Properties object that contains a non-String key or value, the call will fail. Similarly, the call to thepropertyNames orlist method will fail if it is called on a "compromised"Properties object that contains a non-String key.
Theload(Reader)/store(Writer, String) methods load and store properties from and to a character based stream in a simple line-oriented format specified below. Theload(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 ofThe Java™ Language Specification; 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.
TheloadFromXML(InputStream) andstoreToXML(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) isnot 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 singleProperties object without the need for external synchronization.
| Modifier and Type | Field | Description |
|---|---|---|
protectedProperties | 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(Properties defaults) | Creates an empty property list with the specified defaults. |
| Modifier and Type | Method | Description |
|---|---|---|
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 byte stream. |
void | load(Reader reader) | Reads a property list (key and element pairs) from the input character stream in a simple line-oriented format. |
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 thestoreToXML(OutputStream os, String comment) method. |
Object | setProperty(String key,String value) | Calls theHashtable 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 aProperties table using theload(InputStream) method. |
void | store(Writer writer,String comments) | Writes this property list (key and element pairs) in this Properties table to the output character stream in a format suitable for using theload(Reader) 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. |
Set<String> | stringPropertyNames() | Returns a set of keys in 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,forEach,get,getOrDefault,hashCode,isEmpty,keys,keySet,merge,put,putAll,putIfAbsent,rehash,remove,remove,replace,replace,replaceAll,size,toString,valuesprotected Properties defaults
public Properties()
public Properties(Properties defaults)
defaults - the defaults.public Object setProperty(String key,String value)
put. Provided for parallelism with thegetProperty method. Enforces use of strings for property keys and values. The value returned is the result of theHashtable call toput.key - the key to be placed into this property list.value - the value corresponding tokey.null if it did not have one.getProperty(java.lang.String)public void load(Reader reader) throwsIOException
Properties are processed in terms of lines. There are two kinds of line,natural lines andlogical 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-white space 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 affect 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 isnot 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) encodesn 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 :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 arenot 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 ofThe Java™ Language Specification). The differences from the character escape sequences and Unicode escapes used for characters and strings are:
\b doesnot 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.public void load(InputStream inStream) throwsIOException
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 ofThe 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.@Deprecatedpublic void save(OutputStream out,String comments)
store(OutputStream out, String comments) method or thestoreToXML(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 thisProperties object contains any keys or values that are notStrings.public void store(Writer writer,String comments) throwsIOException
Properties table to the output character stream in a format suitable for using theload(Reader) method. Properties from the defaults table of thisProperties table (if any) arenot 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, thecomments 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 in comments is replaced by a line separator generated by theWriter and if the next character in comments is not character# or character! then an ASCII# is written out after that line separator.
Next, a comment line is always written, consisting of an ASCII# character, the current date and time (as if produced by thetoString method ofDate for the current time), and a line separator as generated by theWriter.
Then every entry in thisProperties 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.
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 anIOException.ClassCastException - if thisProperties object contains any keys or values that are notStrings.NullPointerException - ifwriter is null.public void store(OutputStream out,String comments) throwsIOException
Properties table to the output stream in a format suitable for loading into aProperties table using theload(InputStream) method. Properties from the defaults table of thisProperties table (if any) arenot written out by this method.
This method outputs the comments, properties keys and values in the same format as specified instore(Writer), with the following differences:
\uxxxx for their appropriate unicode hexadecimal valuexxxx.\u0020 and characters greater than\u007E in property keys or values are written as\uxxxx for the appropriate hexadecimal valuexxxx.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 anIOException.ClassCastException - if thisProperties object contains any keys or values that are notStrings.NullPointerException - ifout is null.public void loadFromXML(InputStream in) throwsIOException,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 anIOException.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 - ifin is null.storeToXML(OutputStream, String, String),Character Encoding in Entitiespublic void storeToXML(OutputStream os,String comment) throwsIOException
An invocation of this method of the formprops.storeToXML(os, comment) behaves in exactly the same way as the invocationprops.storeToXML(os, comment, "UTF-8");.
os - the output stream on which to emit the XML document.comment - a description of the property list, ornull if no comment is desired.IOException - if writing to the specified output stream results in anIOException.NullPointerException - ifos is null.ClassCastException - if thisProperties object contains any keys or values that are notStrings.loadFromXML(InputStream)public void storeToXML(OutputStream os,String comment,String encoding) throwsIOException
The XML document will have the following DOCTYPE declaration:
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
If the specified comment isnull 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.
os - the output stream on which to emit the XML document.comment - a description of the property list, ornull if no comment is desired.encoding - the name of a supported character encodingIOException - if writing to the specified output stream results in anIOException.UnsupportedEncodingException - if the encoding is not supported by the implementation.NullPointerException - ifos isnull, or ifencoding isnull.ClassCastException - if thisProperties object contains any keys or values that are notStrings.loadFromXML(InputStream),Character Encoding in Entitiespublic String getProperty(String key)
null if the property is not found.key - the property key.setProperty(java.lang.String, java.lang.String),defaultspublic String getProperty(String key,String defaultValue)
key - the hashtable key.defaultValue - a default value.setProperty(java.lang.String, java.lang.String),defaultspublic Enumeration<?> propertyNames()
ClassCastException - if any key in this property list is not a string.Enumeration,defaults,stringPropertyNames()public Set<String> stringPropertyNames()
The returned set is not backed by theProperties object. Changes to thisProperties are not reflected in the set, or vice versa.
defaultspublic 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.