📅 最后修改于: 2020-10-13 00:42:46 🧑 作者: Mango
属性对象包含作为字符串的键和值对。 java.util.Properties类是Hashtable的子类。
它可以用于基于属性键获取属性值。 Properties类提供了从属性文件中获取数据并将数据存储到属性文件中的方法。而且，它可以用来获取系统的属性。
如果从属性文件中更改了信息，则不需要重新编译：如果从属性文件中更改了任何信息，则无需重新编译java类。它用于存储经常更改的信息。
| Method | Description |
|---|---|
| Properties() | It creates an empty property list with no default values. |
| Properties(Properties defaults) | It creates an empty property list with the specified defaults. |
下面给出了Properties类的常用方法。
| Method | Description |
|---|---|
| public void load(Reader r) | It loads data from the Reader object. |
| public void load(InputStream is) | It loads data from the InputStream object |
| public void loadFromXML(InputStream in) | It is used to load all of the properties represented by the XML document on the specified input stream into this properties table. |
| public String getProperty(String key) | It returns value based on the key. |
| public String getProperty(String key, String defaultValue) | It searches for the property with the specified key. |
| public void setProperty(String key, String value) | It calls the put method of Hashtable. |
| public void list(PrintStream out) | It is used to print the property list out to the specified output stream. |
| public void list(PrintWriter out)) | It is used to print the property list out to the specified output stream. |
| public Enumeration propertyNames()) | It returns an enumeration of all the keys from the property list. |
| public Set |
It returns a set of keys in from property list where the key and its corresponding value are strings. |
| public void store(Writer w, String comment) | It writes the properties in the writer object. |
| public void store(OutputStream os, String comment) | It writes the properties in the OutputStream object. |
| public void storeToXML(OutputStream os, String comment) | It writes the properties in the writer object for generating XML document. |
| public void storeToXML(Writer w, String comment, String encoding) | It writes the properties in the writer object for generating XML document with the specified encoding. |
要从属性文件中获取信息，请首先创建属性文件。
user=system
password=oracle
现在，让我们创建java类以从属性文件中读取数据。
import java.util.*;
import java.io.*;
public class Test {
public static void main(String[] args)throws Exception{
FileReader reader=new FileReader("db.properties");
Properties p=new Properties();
p.load(reader);
System.out.println(p.getProperty("user"));
System.out.println(p.getProperty("password"));
}
}
Output:system
oracle
现在，如果您更改属性文件的值，则无需重新编译java类。这意味着没有维护问题。
通过System.getProperties()方法，我们可以获得系统的所有属性。让我们创建一个从系统属性获取信息的类。
import java.util.*;
import java.io.*;
public class Test {
public static void main(String[] args)throws Exception{
Properties p=System.getProperties();
Set set=p.entrySet();
Iterator itr=set.iterator();
while(itr.hasNext()){
Map.Entry entry=(Map.Entry)itr.next();
System.out.println(entry.getKey()+" = "+entry.getValue());
}
}
}
Output:
java.runtime.name = Java(TM) SE Runtime Environment
sun.boot.library.path = C:\Program Files\Java\jdk1.7.0_01\jre\bin
java.vm.version = 21.1-b02
java.vm.vendor = Oracle Corporation
java.vendor.url = http://java.oracle.com/
path.separator = ;
java.vm.name = Java HotSpot(TM) Client VM
file.encoding.pkg = sun.io
user.country = US
user.script =
sun.java.launcher = SUN_STANDARD
...........
现在，让我们编写代码以创建属性文件。
import java.util.*;
import java.io.*;
public class Test {
public static void main(String[] args)throws Exception{
Properties p=new Properties();
p.setProperty("name","Sonoo Jaiswal");
p.setProperty("email","sonoojaiswal@javatpoint.com");
p.store(new FileWriter("info.properties"),"Javatpoint Properties Example");
}
}
让我们看看生成的属性文件。
#Javatpoint Properties Example
#Thu Oct 03 22:35:53 IST 2013
email=sonoojaiswal@javatpoint.com
name=Sonoo Jaiswal