Find Out the Differences between Two Objects in Java

This post demonstrates how to identify and list the differences between two objects using a set of classes and interfaces from Apache Commons Lang.

Classes, Intefaces, and pom.xml

The classes and interfaces to be used for this post are as follow:

org.apache.commons.lang3.builder.Diff
org.apache.commons.lang3.builder.DiffResult
org.apache.commons.lang3.builder.DiffBuilder
org.apache.commons.lang3.builder.Diffable
org.apache.commons.lang3.builder.ToStringStyle

We are using commons-lang3 version 3.6. We also use Java 8.

...
  <dependencies>
	<!-- https://mvnrepository.com/artifact/org.apache.commons/commons-lang3 -->
	<dependency>
	    <groupId>org.apache.commons</groupId>
	    <artifactId>commons-lang3</artifactId>
	    <version>3.6</version>
	</dependency>
  </dependencies>
...

...

<groupId>org.apache.commons</groupId>

<artifactId>commons-lang3</artifactId>

</dependency>

</dependencies>

...

Scenario

We have two blog posts for our use case, and we need to list the differences between them. The list must show the affected field and the old-new (from post 1 to post 2) values.

Blog Post 1

For the first blog post, we have the following data.

Title = First Post
Content = This is my first post
Except = My Blog Post

Blog Post 2

For the second blog post, we have the following data.

Title = Second Post
Content = This is my second post
My Blog Post

The only difference between them is their titles and contents. Let’s list out the difference using some Java codes.

Java Codes

BlogPost class

It is a Java Bean that represents a blog post. Two things worth highlighting in these codes.

The class implements the Diffable interface
The class overrides the diff method
- This is where the magic happens

package com.turreta.apache.commons.lang.diffable;

import org.apache.commons.lang3.builder.DiffBuilder;
import org.apache.commons.lang3.builder.DiffResult;
import org.apache.commons.lang3.builder.Diffable;
import org.apache.commons.lang3.builder.ToStringStyle;

public class BlogPost implements Diffable<BlogPost>{

	private String title;
	private String content;
	private String excerpt;
	
	public String getTitle() {
		return title;
	}

	public void setTitle(String title) {
		this.title = title;
	}

	public String getContent() {
		return content;
	}

	public void setContent(String content) {
		this.content = content;
	}

	public String getExcerpt() {
		return excerpt;
	}

	public void setExcerpt(String excerpt) {
		this.excerpt = excerpt;
	}

	@Override
	public DiffResult diff(BlogPost obj) {
	     return new DiffBuilder(this, obj, ToStringStyle.SHORT_PREFIX_STYLE)
	       .append("title", this.title, obj.title)
	       .append("content", this.content, obj.content)
	       .append("excerpt", this.excerpt, obj.excerpt)
	       .build();
	}
}

package com.turreta.apache.commons.lang.diffable;

import org.apache.commons.lang3.builder.DiffBuilder;

import org.apache.commons.lang3.builder.DiffResult;

import org.apache.commons.lang3.builder.Diffable;

import org.apache.commons.lang3.builder.ToStringStyle;

public class BlogPost implements Diffable<BlogPost>{

private String title;

private String content;

private String excerpt;

public String getTitle() {

return title;

}

public void setTitle(String title) {

this.title = title;

}

public String getContent() {

return content;

}

public void setContent(String content) {

this.content = content;

}

public String getExcerpt() {

return excerpt;

}

public void setExcerpt(String excerpt) {

this.excerpt = excerpt;

}

@Override

public DiffResult diff(BlogPost obj) {

return new DiffBuilder(this, obj, ToStringStyle.SHORT_PREFIX_STYLE)

.append("title", this.title, obj.title)

.append("content", this.content, obj.content)

.append("excerpt", this.excerpt, obj.excerpt)

.build();

}

DiffableDemo class

This is the main class – the entry point.

package com.turreta.apache.commons.lang.diffable;

import org.apache.commons.lang3.builder.Diff;
import org.apache.commons.lang3.builder.DiffResult;

public class DiffableDemo {

	public static void main(String[] args) {
		BlogPost postOne = new BlogPost();
		postOne.setTitle("First Post");
		postOne.setContent("This is my first post");
		postOne.setExcerpt("My Blog Post");
		
		BlogPost postTwo = new BlogPost();
		postTwo.setTitle("Second Post");
		postTwo.setContent("This is my second post");
		postTwo.setExcerpt("My Blog Post");
		
		
		DiffResult diff = postOne.diff(postTwo);
		
		for(Diff<?> d: diff.getDiffs()) {
			System.out.println(d.getFieldName() 
                            + "= FROM[" + d.getLeft() + "] TO [" + d.getRight() + "]");
		}
		
		System.out.println();
	}
}

package com.turreta.apache.commons.lang.diffable;

import org.apache.commons.lang3.builder.Diff;

import org.apache.commons.lang3.builder.DiffResult;

public class DiffableDemo {

public static void main(String[] args) {

BlogPost postOne = new BlogPost();

postOne.setTitle("First Post");

postOne.setContent("This is my first post");

postOne.setExcerpt("My Blog Post");

BlogPost postTwo = new BlogPost();

postTwo.setTitle("Second Post");

postTwo.setContent("This is my second post");

postTwo.setExcerpt("My Blog Post");

DiffResult diff = postOne.diff(postTwo);

for(Diff<?> d: diff.getDiffs()) {

System.out.println(d.getFieldName()

+ "= FROM[" + d.getLeft() + "] TO [" + d.getRight() + "]");

}

System.out.println();

}

This outputs:

title= FROM[First Post] TO [Second Post]
content= FROM[This is my first post] TO [This is my second post]

1 2	title= FROM[First Post] TO [Second Post] content= FROM[This is my first post] TO [This is my second post]