Java main properties file

Java Property File Processing

Properties is a file extension for files mainly used in Java related technologies to store the configurable parameters of an application. Java Properties files are amazing resources to add information in Java. Generally, these files are used to store static information in key and value pair. Things that you do not want to hard code in your Java code goes into properties files. The advantage of using properties file is we can configure things which are prone to change over a period of time without the need of changing anything in code. Properties file provide flexibility in terms of configuration. Sample properties file is shown below, which has information in key-value pair.

Each parameter is stored as a pair of strings, left side of equal (=) sign is for storing the name of the parameter (called the key), and the other storing the value.

Configuration:

This is property file having my configuration FileName=Data.txt Author_Name=Amit Himani Website=w3resource.com Topic=Properties file Processing 

First Line which starts with # is called comment line. We can add comments in properties which will be ignored by java compiler.

Below is the java program for reading above property file.

package propertiesfile; import java.io.FileInputStream; import java.io.IOException; import java.util.Properties; public class PropertyFileReading < public static void main(String[] args) < Properties prop = new Properties(); try < // load a properties file for reading prop.load(new FileInputStream("myConfig.properties")); // get the properties and print prop.list(System.out); //Reading each property value System.out.println(prop.getProperty("FileName")); System.out.println(prop.getProperty("Author_Name")); System.out.println(prop.getProperty("Website")); System.out.println(prop.getProperty("TOPIC")); >catch (IOException ex) < ex.printStackTrace(); >> > 

The program uses load( ) method to retrieve the list. When the program executes, it first tries to load the list from a file called myConfig.properties. If this file exists, the list is loaded else IO exception is thrown.

If File is not present in default project root location, we will get an exception like below, We can provide a fully qualified path of the file as well.

Use of getProperties() Method

One useful capability of the Properties class is that you can specify a default property that will be returned if no value is associated with a certain key. For example, a default value can be specified along with the key in the getProperty( ) method—such as getProperty(“name”,“default value”). If the “name” value is not found, then “default value” is returned. When you construct a Properties object, you can pass another instance of Properties to be used as the default properties for the new instance.

Writing Properties file

At any time, you can write a Properties object to a stream or read it back. This makes property lists especially convenient for implementing simple databases. For Example below program writes states can capital cities. “capitals.properties” file having state name as keys and state capital as values.

package propertiesfile; import java.io.FileOutputStream; import java.io.IOException; import java.util.Properties; public class PropertyFileWriting < public static void main(String args[]) < Properties prop = new Properties(); try < // set the properties value prop.setProperty("Gujarat", "Gandhinagar"); prop.setProperty("Maharashtra", "Mumbai"); prop.setProperty("Madhya_Pradesh", "Indore"); prop.setProperty("Rajasthan", "Jaipur"); prop.setProperty("Punjab", "mkyong"); prop.setProperty("Uttar_Pradesh", "Lucknow"); // save properties to project root folder prop.store(new FileOutputStream("capitals.properties"), null); >catch (IOException ex) < ex.printStackTrace(); >> > 

After running the program we can see a new file created named “capitals.properties” under project root folder as shown below.

Web Apr 24 19:50:18 IST 2013 Uttar_Pradesh=Lucknow Madhyar_Pradesh=Indore Maharashtra=Mumbai Gujarat=Gandhinagar Panjab=mkyong Rajasthan=jaipur

• Properties file provide flexibility in terms of configuration in java based application.
• We can store information in a properties file which can be changed over a period of time like database connection properties, password, input file name or location etc.
• We can Read/Write property file using java.util.Properties library of Java.

Java Code Editor:

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Простой пример работы с Property файлами в Java

Property файлы присутствуют практически в каждом проекте, и сейчас я вам покажу простой пример их использования, а также расскажу, зачем они и где используются.

Шаг 0. Создание проекта

Начнем с того что создадим простой Maven проект, указав название и имя пакета:

Структура, которая получится в конце проекта довольно таки простая.

Как видите у нас только два файла, первый – Main.java, а второй – config.properties.

Шаг 2. Добавляем конфигурационные данные в проперти файл

Проперти файлы либо файлы свойств – предназначены, для того чтобы хранить в них какие-то статические данные необходимые проект, например логин и пароль к БД.

Давайте добавим в наш config.properties логин и пароль (это любые данные, для того чтобы продемонстрировать работу с property файлами).

Содержимое config.properties:

db.host = http://localhost:8888/mydb db.login = root db.password = dbroot

ключ> – это уникальное имя, по которому можно получить доступ к значению, хранимому под этим ключом.

значение> – это текст, либо число, которое вам необходимо для выполнения определённой логики в вашей программе.

Шаг 3. Получаем Property данные

Как можно видеть в структуре проекта выше, там есть класс Main.java давайте его создадим и напишем в нем следующее:

package com.devcolibir.prop; import java.io.*; import java.util.Properties; public class Main < public static void main(String[] args) < FileInputStream fis; Properties property = new Properties(); try < fis = new FileInputStream("src/main/resources/config.properties"); property.load(fis); String host = property.getProperty("db.host"); String login = property.getProperty("db.login"); String password = property.getProperty("db.password"); System.out.println("HOST: " + host + ", LOGIN: " + login + ", PASSWORD: " + password); >catch (IOException e) < System.err.println("ОШИБКА: Файл свойств отсуствует!"); >> >

Обращаясь к property.getProperty(ключ>) – вы получаете его значение.

Вот такой краткий, но думаю познавательный урок.

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Java Guides

This is a common task for a developer to maintain project configuration data or settings in an external file, for example keeping JDBC database configurations in the database.properties file.

In this tutorial, we will show you how to read and write to/from a database.properties file.

1. Write to Properties File Example

Let’s write a Java program to set the property key and value, and save it to a specific location. In this example, we will use the «database.properties» path. In the next example, we will read or load the same file.

package com.javaguides.collections.properties; import java.io.FileOutputStream; import java.io.IOException; import java.io.OutputStream; import java.util.Properties; public class WritePropertyFile < public static void main(String[] args) < try (OutputStream output = new FileOutputStream("database.properties")) < Properties prop = new Properties(); // set the properties value prop.setProperty("jdbc.driverClassName", "com.mysql.jdbc.Driver"); prop.setProperty("jdbc.url", "jdbc:mysql://localhost:3306/demo?useSSL=false"); prop.setProperty("jdbc.username", "root"); prop.setProperty("jdbc.password", "root"); // save properties to project root folder prop.store(output, null); // Java 8 , print key and values prop.forEach((key, value) -> System.out.println("Key : " + key + ", Value : " + value)); > catch (IOException io) < io.printStackTrace(); > > >

Key : jdbc.driverClassName, Value : com.mysql.jdbc.Driver Key : jdbc.password, Value : root Key : jdbc.username, Value : root Key : jdbc.url, Value : jdbc:mysql://localhost:3306/demo?useSSL=false 

The «database.properties» file has created under the root directory of your project with the following content —

jdbc.url=jdbc\:mysql\://localhost\:3306/demo?useSSL\=false jdbc.username=root jdbc.password=root jdbc.driverClassName=com.mysql.jdbc.Driver

2. Read or Load a Properties File Example

Let’s read or load properties from the «database.properties» file that created in the above example and print the key-value pair.

package com.javaguides.collections.properties; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; import java.util.Properties; public class ReadPropertyFile < public static void main(String[] args) < try (InputStream input = new FileInputStream("database.properties")) < Properties prop = new Properties(); // load a properties file from InputStream prop.load(input); // Java 8 , print key and values prop.forEach((key, value) -> System.out.println("Key : " + key + ", Value : " + value)); > catch (IOException ex) < ex.printStackTrace(); > > >

Key : jdbc.driverClassName, Value : com.mysql.jdbc.Driver Key : jdbc.password, Value : root Key : jdbc.username, Value : root Key : jdbc.url, Value : jdbc:mysql://localhost:3306/demo?useSSL=false

3. Read or Load a Properties File from Classpath

Let’s keep «database.properties» file in the classpath. Now let’s read or load a properties file database.properties from project classpath, and print the key-value pair.

package com.javaguides.collections.properties; import java.io.IOException; import java.io.InputStream; import java.util.Properties; import java.util.logging.Level; import java.util.logging.Logger; public class ReadPropertyFileFromClassPath < public static void main(String[] args) < String fileName = "database.properties"; ReadPropertyFileFromClassPath obj = new ReadPropertyFileFromClassPath(); Properties prop = obj.loadProperties(fileName); // Java 8 , print key and values prop.forEach((key, value) -> System.out.println("Key : " + key + ", Value : " + value)); > public Properties loadProperties(String fileName) < Properties prop = new Properties(); try (InputStream inputStream = ReadPropertyFileFromClassPath.class.getClassLoader() .getResourceAsStream(fileName)) < // check for null if (inputStream == null) < System.out.println("Unable to find " + fileName + " file"); return prop; > // load a properties file from class path prop.load(inputStream); > catch (IOException e) < Logger.getLogger(getClass().getName()).log(Level.SEVERE, e.getMessage(), e); > return prop; > >

Key : jdbc.driverClassName, Value : com.mysql.jdbc.Driver Key : jdbc.password, Value : root Key : jdbc.username, Value : root Key : jdbc.url, Value : jdbc:mysql://localhost:3306/demo?useSSL=false

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Java Properties File: How to Read config.properties Values in Java?

.properties is a file extension for files mainly used in Java related technologies to store the configurable parameters of an application. They can also be used for storing strings for Internationalization and localization; these are known as Property Resource Bundles.

Each parameter is stored as a pair of strings, one storing the name of the parameter (called the key/map ), and the other storing the value.

Below is a sample Java program which demonstrate you how to retrieve/read config.properties values in Java. For update follow this tutorial.

We will create 3 files:

1. CrunchifyReadConfigMain.java
2. CrunchifyGetPropertyValues.java
3. config.properties file

Main Class (CrunchifyReadConfigMain.java) which will call getPropValues() method from class CrunchifyGetPropertyValues.java .

Let’s get started:

Step-1: Create config.properties file.

1. Create Folder “ resources ” under Java Resources folder if your project doesn’t have it.
2. create config.properties file with below value.

/Java Resources/config.properties file content:

#Crunchify Properties user=Crunchify company1=Google company2=eBay company3=Yahoo

Step-2

Create file CrunchifyReadConfigMain.java

package crunchify.com.tutorial; import java.io.IOException; /** * @author Crunchify.com * */ public class CrunchifyReadConfigMain < public static void main(String[] args) throws IOException < CrunchifyGetPropertyValues properties = new CrunchifyGetPropertyValues(); properties.getPropValues(); >>

Step-3

Create file CrunchifyGetPropertyValues.java

package crunchify.com.tutorial; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStream; import java.util.Date; import java.util.Properties; /** * @author Crunchify.com * */ public class CrunchifyGetPropertyValues < String result = ""; InputStream inputStream; public String getPropValues() throws IOException < try < Properties prop = new Properties(); String propFileName = "config.properties"; inputStream = getClass().getClassLoader().getResourceAsStream(propFileName); if (inputStream != null) < prop.load(inputStream); >else < throw new FileNotFoundException("property file '" + propFileName + "' not found in the classpath"); >Date time = new Date(System.currentTimeMillis()); // get the property value and print it out String user = prop.getProperty("user"); String company1 = prop.getProperty("company1"); String company2 = prop.getProperty("company2"); String company3 = prop.getProperty("company3"); result = "Company List = " + company1 + ", " + company2 + ", " + company3; System.out.println(result + "\nProgram Ran on " + time + " by user=" + user); > catch (Exception e) < System.out.println("Exception: " + e); >finally < inputStream.close(); >return result; > >

Step-4

Run CrunchifyReadConfigMain and checkout result.

Company List = Google, eBay, Yahoo Program Ran on Mon May 13 21:54:55 PDT 2013 by user=Crunchify

As usually happy coding and enjoy. Do let me know if you see any exception. List of all Java Tutorials.

Are you running above program in IntelliJ IDE and getting NullPointerException?

Please follow below tutorial for fix.

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