Properties class in Java

The properties object contains key and value pair both as a string. It is the subclass of Hashtable.

It can be used to get property value based on the property key. The Properties class provides methods to get data from properties file and store data into properties file. Moreover, it can be used to get properties of system.

Advantage of properties file

Easy Maintenance: If any information is changed from the properties file, you don't need to recompile the java class. It is mainly used to contain variable information i.e. to be changed.

Methods of Properties class

The commonly used methods of Properties class are given below.

Method	Description
public void load(Reader r)	loads data from the Reader object.
public void load(InputStream is)	loads data from the InputStream object
public String getProperty(String key)	returns value based on the key.
public void setProperty(String key,String value)	sets the property in the properties object.
public void store(Writer w, String comment)	writers the properties in the writer object.
public void store(OutputStream os, String comment)	writes the properties in the OutputStream object.
storeToXML(OutputStream os, String comment)	writers the properties in the writer object for generating xml document.
public void storeToXML(Writer w, String comment, String encoding)	writers the properties in the writer object for generating xml document with specified encoding.

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Example of Properties class to get information from properties file

To get information from the properties file, create the properties file first.

db.properties

1. user=system  
2. password=oracle  

Now, lets create the java class to read the data from the properties file.

Test.java

1. import java.util.*;  
2. import java.io.*;  
3. public class Test {  
4. public static void main(String[] args)throws Exception{  
5.     FileReader reader=new FileReader("db.properties");  
6.       
7.     Properties p=new Properties();  
8.     p.load(reader);  
9.       
10.     System.out.println(p.getProperty("user"));  
11.     System.out.println(p.getProperty("password"));  
12. }  
13. }  

Output:system
       oracle

Now if you change the value of the properties file, you don't need to compile the java class again. That means no maintenance problem.

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Example of Properties class to get all the system properties

By System.getProperties() method we can get all the properties of system. Let's create the class that gets information from the system properties.

Test.java

1. import java.util.*;  
2. import java.io.*;  
3. public class Test {  
4. public static void main(String[] args)throws Exception{  
5.   
6. Properties p=System.getProperties();  
7. Set set=p.entrySet();  
8.   
9. Iterator itr=set.iterator();  
10. while(itr.hasNext()){  
11. Map.Entry entry=(Map.Entry)itr.next();  
12. System.out.println(entry.getKey()+" = "+entry.getValue());  
13. }  
14.   
15. }  
16. }  

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
...........

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Example of Properties class to create properties file

Now lets write the code to create the properties file.

Test.java

1. import java.util.*;  
2. import java.io.*;  
3. public class Test {  
4. public static void main(String[] args)throws Exception{  
5.   
6. Properties p=new Properties();  
7. p.setProperty("name","Kundan Signh");  
8. p.setProperty("email","kundan*****@**.com");  
9.   
10. p.store(new FileWriter("info.properties"),"Kundan Properties");  
11.   
12. }  
13. }  

Let's see the generated properties file.

info.properties

1. #Kundan Properties  
2. #Sun Feb 22 10:35:53 IST 2015  
3. email=kundan*****@**.com  
4. name=Kundan Singh