Java read object properties

Properties File — Java Read & Write

This tutorial explains step by step to read and write a properties file in java with example You learned to read properties file with key and values as well as line by line and also write key and values to the properties file.

In this tutorial, How to read and write a properties file content in Java

Java properties file reader example

In this example, you will learn how to read a key and its values from a properties file and display it to console

Let’s declare the properties file

Create a properties object, Properties is a data structure to store keys and values in java

Create URL object using ClassLoader . getSystemResource method

Create a InputStream using url.openStream method

Load the properties content into the java properties object using the load method

Add try and catch block for IOExceptions and FIleNotFoundException

Oneway, Print the value using getProperty with the key of a properties object

Another way is to iterate properties object for the loop

First, get all keys using stringPropertyNames

using for loop print the key and values.

 catch (FileNotFoundException fie) < fie.printStackTrace(); >catch (IOException e) < e.printStackTrace(); >System.out.println(properties.getProperty("hostname")); Set keys = properties.stringPropertyNames(); for (String key : keys) < System.out.println(key + " - " + properties.getProperty(key)); >> > 

How to read a properties file line by line in java

• created a File object with an absolute path
• Create BufferedReader using FileReader object
• get the First line of the properties file using readLine of BufferedReader
• Loop using while loop until the end of the line reached
• Print each line

 > catch (FileNotFoundException e1) < e1.printStackTrace(); >catch (IOException e) < e.printStackTrace(); >finally < try < br.close(); >catch (IOException e) < e.printStackTrace(); >> > > 

How to write a key and values to a properties file in java

In this example, You can read and write a property using

• First create a File object
• Create a writer object using FileWriter
• Create properties object and add new properties or update existing properties if the properties file exists
• setProperties method do update or add key and values
• store method of properties object writes to the properties file, You have to add the comment which appends to the properties file as a comment

Here is a complete example read and write a properties file

 catch (FileNotFoundException e) < e.printStackTrace(); >catch (IOException e) < e.printStackTrace(); >> > 

Conclusion

You learned to read a properties file with keys and values as well as line by line and also write keys and values to the properties file

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How to read the data from a properties file in Java?

The Properties is a subclass of Hashtable class and it 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.

The Properties file can be used in Java to externalize the configuration and to store the key-value pairs. The Properties.load() method of Properties class is convenient to load .properties file in the form of key-value pairs.

Syntax

public class Properties extends Hashtable

credentials.properties file

Example

import java.io.*; import java.util.*; public class ReadPropertiesFileTest < public static void main(String args[]) throws IOException < Properties prop = readPropertiesFile("credentials.properties"); System.out.println("username: "+ prop.getProperty("username")); System.out.println("password: "+ prop.getProperty("password")); >public static Properties readPropertiesFile(String fileName) throws IOException < FileInputStream fis = null; Properties prop = null; try < fis = new FileInputStream(fileName); prop = new Properties(); prop.load(fis); >catch(FileNotFoundException fnfe) < fnfe.printStackTrace(); >catch(IOException ioe) < ioe.printStackTrace(); >finally < fis.close(); >return prop; > >

Output

username: admin password: admin@123

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How to read properties file in java

In this post , we will see how to read properties file in java.

Properties files are used in java projects to externalise configuration, for example, database settings.

Java uses Properties class to store the above key-values pair. Properties.load() method is very convenient to load properties file in form of key-values pairs.

Properties file looks something like this.

There are two ways you can do it.

Read properties file from System

In this, you need to read properties file from system path. Here I am putting properties file in root level of project.

When you run above program, you will get following output:

Reading from properties file
—————————–
host : localhost
username : java2blog
password : java123
—————————–

Read properties file from classpath

You can read properties file to classpath too. You have $project/src as default classpath as this src folder will be copied to classes. You can put it in $project/src folder and read it from there.

you need to use this.getClass().getResourceAsStream(«/config.properties»); to read it from classpath .

When you run above program, you will get following output:

Reading from properties file
—————————–
host : localhost
username : java2blog
password : java123
—————————–

That’s all about how to read properties file in java

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