A .properties file is a simple collection of key-value pairs that can be parsed by the java.util.Properties class. Properties files are widely used for many purposes in all kinds of Java/j2ee applications, often to store configuration or localization data. And all over the project scripts can then use those properties easily.
There are a numerous ways to manipulate properties file in Java, in this post I’ll be covering the following topics with the code examples.
- Reading properties file from the Class Path
- Reading properties file from the file system
- Writing/Modifying properties file
Create a properties file and place it in project directory.
config.properties
dburl=jdbc:oracle:thin:@127.0.0.0:1521:mycart dbuser=mycart_user dbpassword=Password@69
1. Reading properties file from the Class Path
Note: The java.lang.ClassLoader.getResourceAsStream() method returns an input stream for reading the specified resource..
One way to read properties file in Java is to load it from the file system.
Project Structure
ClassPathProperties.java
package com.rmpk.prj;
import java.io.IOException;
import java.io.InputStream;
import java.text.MessageFormat;
import java.util.Properties;
import java.util.logging.Logger;
public class ClassPathProperties {
private static final Logger LOGGER =
Logger.getLogger(ClassPathProperties.class.getName());
public ClassPathProperties() {
loadProperties();
}
private Properties loadProperties() {
Properties prop = new Properties();
InputStream input = null;
try {
// Properties file read from outside class path
String filePath = "config.properties";
// load the file handle for class path
input = this.getClass().getClassLoader().getResourceAsStream(filePath);
// load a properties file
prop.load(input);
// Read earch properties by key
String dburl = prop.getProperty("dburl");
String dbpassword = prop.getProperty("dbpassword");
String dbuser = prop.getProperty("dbuser");
LOGGER.info(MessageFormat.format("dburl : {0}, dbpassword : {1}, "
+ "dbuser : {2}", dburl, dbpassword, dbuser));
// Print properties in java 8
prop.forEach((key, val) -> {
LOGGER.info(MessageFormat.format("Key : {0}, Value : {1}", key, val));
});
} catch (Exception e) {
e.printStackTrace();
LOGGER.warning(e.getCause().getMessage());
} finally {
if (input != null) {
try {
input.close();
} catch (IOException e) {
e.printStackTrace();
LOGGER.warning("loadProperties method IOException: " +
e.getCause().getMessage());
}
}
}
return prop;
}
public static void main(String[] args) {
ClassPathProperties p = new ClassPathProperties();
}
}
The output of the preceding code is as follows:
2. Reading properties file from the file system
Note: A property list can contain another property list as its "defaults"; this second property list is searched if the property key is not found in the original property list. .
If you have properties file in the project classpath then you can load it by using the getResourceAsStream method. That is another way to read properties file in Java.
Project Structure
FileSystemProperties.java
package com.rmpk.proj;
import java.io.FileInputStream;
import java.io.IOException;
import java.text.MessageFormat;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;
public class FileSystemProperties {
private static final Logger LOGGER =
Logger.getLogger(FileSystemProperties.class.getName());
private static Properties loadProperties() {
Properties prop = new Properties();
FileInputStream input = null;
try {
// Properties file read from outside class path
// String filePath = "resources/config.properties";
String filePath = "config.properties";
// load the file handle for main.properties
input = new FileInputStream(filePath);
// load a properties file
prop.load(input);
// Read earch properties by key
String dburl = prop.getProperty("dburl");
String dbpassword = prop.getProperty("dbpassword");
String dbuser = prop.getProperty("dbuser");
LOGGER.info(MessageFormat.format("dburl : {0}, dbpassword : {1}, "
+ "dbuser : {2}", dburl, dbpassword, dbuser));
// Print properties in java 8
prop.forEach((key, val) -> {
LOGGER.info(MessageFormat.format("Key : {0}, Value : {1}", key, val));
});
} catch (Exception e) {
e.printStackTrace();
LOGGER.warning(e.getCause().getMessage());
} finally {
if (input != null) {
try {
input.close();
} catch (IOException e) {
e.printStackTrace();
LOGGER.warning("loadProperties method IOException: " +
e.getCause().getMessage());
}
}
}
return prop;
}
public static void main(String[] args) {
LOGGER.setLevel(Level.ALL);
loadProperties();
}
}
The output of the preceding code is as follows:
