How to use Java properties file - Learning Java

By Sergey Skudaev

In this tutorial you will learn how to use Java properties file to pass parameters to java application. There are four Java code examples that show different approaches to problem solution and explain how to write Java code that read parameters from properties file. Read Start Java Programming tutorial to learn how to configure your PC to be able to run java application.

Copy Greeting2.java source code and paste it in notepad or your favorite editor for plain text. (Do not use MS World).

Greeting2.java

import java.io.*;
import java.util.*;

public class Greeting2
{
String message;

// class constructor

public Greeting2()
{

}

public void setMessage()
{

//create an instance of properties class

Properties props = new Properties();

//try retrieve data from file
try {

props.load(new FileInputStream("message.properties"));

message = props.getProperty("message");

System.out.println(message);
}

//catch exception in case properties file does not exist

             catch(IOException e)
             {
             e.printStackTrace();
             }
     }

     public static void main(String[] args)
     {
     //create an instance of greeting2 class

Greeting2 gr = new Greeting2();

//call the setMessage() method of the Greeting2 class

gr.setMessage();

}
} //end of source code file

Save the Greeting2.java file in "C:\java\prop" directory

Compile the source file Greeting2.java

C:\java\prop>javac Greeting2.java
Execute Greeting2 Java application

     C:\java\prop>java Greeting2
     java.io.FileNotFoundException: message.properties (The system cannot find the
     file specified)
     at java.io.FileInputStream.open(Native Method)
     at java.io.FileInputStream.<init>(FileInputStream.java:106)
     at java.io.FileInputStream.<init>(FileInputStream.java:66)
     at Greeting2.setMessage(Greeting2.java:37)
     at Greeting2.main(Greeting2.java:60)

C:\java\prop>

Input Output Exeption is thrown because message.properties file does not exist.

Let us create it. Open Notepad and type the following text

message = How are you

Save file as message.properties in C:\java\prop directory.

Try to execute Greeting2 application again.

C:\java\prop>java Greeting2
How are you

Now our message is displayed. Open message.properties file and delete the text

message = How are you.

Save the file.

Try to execute Greeting2 application again.

C:\java\prop>java Greeting2
null

C:\java\prop>

null will display instead of message

To improve our program let us add default message,
just in case if something will go wrong with getting message from file

Improved our greeting class

Greeting3.java

import java.io.*;
import java.util.*;

public class Greeting3
{
String message;

public Greeting3()
{

}

     public void setMessage()
     {
     //create an instance of properties class

Properties props = new Properties();

//try retrieve data from file
//catch exception in case properties file does not exist

try {

props.load(new FileInputStream("message.properties"));

message = props.getProperty("message");

//If value of message variable is null assign default value "Hello World"

             if(message==null)
               {
               message=new String("Hello World!");
               }

System.out.println(message);

}

//catch exception in case properties file does not exist

     catch(IOException e)
     {
     e.printStackTrace();
     }
   }

     public static void main(String[] args)
     {
     //create an instance of Greeting3 class

Greeting3 gr = new Greeting3();

//call the setMessage() method of the Greeting3 class

gr.setMessage();

}

Compile the source file Greeting3.java

C:\java\prop>javac Greeting3.java
Execute Greeting3 Java application

C:\java\prop>java Greeting3
Hello World!

Open message.properties file and enter text

message = How are you

Save the file

Execute Greeting3 Java application again

"How are you" message displays

C:\java\prop>java Greeting3
How are you

Let us improve the application. Set default message in class constractor

import java.io.*;
import java.util.*;

public class Greeting4
{
String message;

          public Greeting4()
           {
           message= new String("Hello World");
           }

     public void setMessage()
     {
     //create an instance of properties class

Properties props = new Properties();

//try retrieve data from file

try {

props.load(new FileInputStream("message.properties"));

// assign value to message variable only if it is not null

                  if(props.getProperty("message") !=null)
                    {
                    message = props.getProperty("message");
                    }

System.out.println(message);
}

//catch exception in case properties file does not exist

               catch(IOException e)
               {
                   System.out.println(message);
                   }
     }

     public static void main(String[] args)
     {
     //create an instance of Greeting4 class

Greeting4 gr = new Greeting4();

//call the setMessage() method of the Greeting4 class

gr.setMessage();
}
}

Compile the source file Greeting4.java

C:\java\prop>javac Greeting4.java
Execute Greeting4 Java application

C:\prop\final>java Greeting4
How are you

Open message.properties file and delete text "message = How are you"

Execute Greeting4 Java application again

C:\prop\final>java Greeting4
Hello World

Delete message.properties file

Execute Greeting4 Java application again

C:\prop\final>java Greeting4
Hello World

Hello World default message will be displayed in both cases.

Did you find information useful? Send to your friend a link to this page

Please rate the tutorial

Comments

Computer Programming Web programming Tips

How to use Java properties file - Learning Java