Print all keys with values from a properties file in Java

This post will discuss how to print out all keys with values from a properties file in Java.

The properties file consists of a set of key-value pairs of string type, which can be loaded using the Properties class in Java. There are several ways to list all properties present in a properties file using the Properties class in Java:

1. Using `keySet()` method

Since Properties class extends java.util.Hashtable class, we can use its inherited keySet() method for iterating a Properties object.

The following code prints out the current set of system properties using the keySet() method, where the current system properties are loaded into a Properties object using the getProperties() method of the System class:

import java.util.Properties;

class Main

{

public static void main(String[] args)

{

Properties prop = System.getProperties();

printProperties(prop);

}

public static void printProperties(Properties prop)

{

for (Object key: prop.keySet()) {

System.out.println(key + ": " + prop.getProperty(key.toString()));

}

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In Java 8, we can use Stream to print all system properties, as demonstrated below:

public static void printProperties(Properties prop) {

prop.keySet().stream()

.map(key -> key + ": " + prop.getProperty(key.toString()))

.forEach(System.out::println);

}

2. Using `stringPropertyNames()` method

We can also use the stringPropertyNames() method, which returns a set of keys present in the Properties object.

import java.util.Properties;

class Main

{

public static void main(String[] args)

{

Properties prop = System.getProperties();

printProperties(prop);

}

public static void printProperties(Properties prop)

{

for (String key: prop.stringPropertyNames()) {

System.out.println(key + ": " + prop.getProperty(key));

}

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In Java 8, we can use Stream to list out all the properties, as shown below:

public static void printProperties(Properties prop) {

prop.stringPropertyNames().stream()

.map(key -> key + ": " + prop.getProperty(key))

.forEach(System.out::println);

}

3. Using `propertyNames()` method

Alternatively, we can use the enumeration of all the keys returned by the propertyNames() method, as shown below:

import java.util.Enumeration;

import java.util.Properties;

class Main

{

public static void main(String[] args)

{

Properties prop = System.getProperties();

printProperties(prop);

}

public static void printProperties(Properties prop)

{

Enumeration e = prop.propertyNames();

while (e.hasMoreElements())

{

String key = e.nextElement().toString();

System.out.println(key + ": " + prop.getProperty(key));

}

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4. Overriding `put()` method

Since Properties inherits from Hashtable, the put() method can be applied to a Properties object. The idea is to override the put() method and put each key-value pair into a map. Then we can simply iterate through the map to list out all the properties.

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.util.HashMap;

import java.util.Map;

import java.util.Properties;

class Main

{

public static void main(String[] args)

{

String propertiesFilename = "config.properties"; // load from the filesystem

Map<String, String> properties = new HashMap<>();

try (InputStream stream = new FileInputStream(propertiesFilename))

{

Properties prop = new Properties() {

@Override

public synchronized Object put(Object key, Object value) {

return properties.put(key.toString(), value.toString());

}

};

prop.load(stream);

}

catch (IOException e) {

e.printStackTrace();

}

System.out.println(properties);

}

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5. Using Apache Commons Configuration

For reading the properties file in its original order, we can use third-party libraries like Apache Commons Configuration. Here’s a working example:

import org.apache.commons.configuration.ConfigurationException;

import org.apache.commons.configuration.PropertiesConfiguration;

import org.apache.commons.configuration.PropertiesConfigurationLayout;

import java.util.Set;

class Main

{

public static void main(String[] args)

{

String propertiesFilename = "config.properties"; // load from the classpath

PropertiesConfiguration config = null;

try {

config = new PropertiesConfiguration(propertiesFilename);

} catch (ConfigurationException e) {

e.printStackTrace();

}

PropertiesConfigurationLayout layout = config.getLayout();

printProperties(layout);

}

public static void printProperties(PropertiesConfigurationLayout layout)

{

Set<String> keys = layout.getKeys();

for (String key: keys)

{

String value = layout.getConfiguration().getProperty(key).toString();

System.out.println(key + ": " + value);

}

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That’s all about printing all keys with values from a properties file in Java.

Print all keys with values from a properties file in Java

1. Using keySet() method

2. Using stringPropertyNames() method

3. Using propertyNames() method

4. Overriding put() method

5. Using Apache Commons Configuration

Share this:

1. Using `keySet()` method

2. Using `stringPropertyNames()` method

3. Using `propertyNames()` method

4. Overriding `put()` method