How To Use @ToString Annotation With Project Lombok

Project Lombok Tutorial

How To Use @ToString Annotation With Project Lombok

@ToString annotation enables you to avoid having to manually write a toString() method while inspecting fields for your objects.

Using toString() method can be an essential tool while debugging your object fields.

# Dev Environment:

Apache maven (v3.6.1)
maven-compiler-plugin (v3.8.1)
lombok (v1.18.8)
Apache Netbeans (v10.0)

TIP: For those who would like to follow along with this blog, just clone my repository git clone https://github.com/steven7mwesigwa/java-tutorials.git and navigate to java-tutorials\project-lombok\tostring. In there, you should be able to play around with all the source code used in this blog post.

# Terminologies

public String toString()

toString() method is used to return a string representation of an object.

This method typically returns a string consisting the class name of the object, an "@" character and an unsigned hexadecimal representation of the hash code of the object. i.e com.stevenmwesigwa.tostring.demo1.Person@15db9742.

TIP: This method can be overridden to return a more informative representation of object fields. i.e Person{firstname=Steven, lastname=Mwesigwa}.

# Demonstration : (Without Lombok)

Let's create a Person class that will have a manual implementation of our toString() method. Full code here


//demo1
package com.stevenmwesigwa.tostring.demo1;

public class Person {

    private String firstname;
    private String lastname;

    public void setFirstName(String firstname) {
        this.firstname = firstname;
    }

    public void setLastName(String lastname) {
        this.lastname = lastname;
    }

    @Override
    public String toString() {
        return "Person{" + "firstname=" + firstname + ", lastname=" + lastname + '}';
    }
}

When we create and run an App.java class that makes use of this Person class Full code here, we successfully return a string representation of our Person object. i.e Person{firstname=Steven, lastname=Mwesigwa}

This is fine. But with @ToString annotation from project lombok library, we don't have to manually implement toString() methods for our objects any more.

# Demonstration : (With Lombok)

Let's create a Person class but this time using @ToString annotation... . Full code here


//demo2
package com.stevenmwesigwa.tostring.demo2;

import lombok.ToString;

@ToString
public class Person {

    private String firstname;
    private String lastname;

    public void setFirstName(String firstname) {
        this.firstname = firstname;
    }

    public void setLastName(String lastname) {
        this.lastname = lastname;
    }
}

By adding @ToString annotation, a respective toString() method will be added for us automatically.

Now here is what's even more interesting, You're not limited to this option only. Lombok provides us other options to customize how we want to return string representations of our object fields. Let's look at some of these.

# How To use `IncludeFieldNames` Configuration Key With @ToString annotation

Depending on your use case, you may not want to have field names to be part of the returned string representation of your object fields. This is what lombok.toString.includeFieldNames configuration key is for.

By default, it's value is true . Meaning all non-static field names with their values will be returned. Setting it's value to false will make lombok not display non-static field names and simply return a list of all non-static field values separated by commas. i.e Person(Steven, Mwesigwa)

Let's create a Person class to demonstrate this. Full code here


//demo3
package com.stevenmwesigwa.tostring.demo3;

import lombok.ToString;

@ToString(includeFieldNames=false)
public class Person {

    private String firstname;
    private String lastname;

    public void setFirstName(String firstname) {
        this.firstname = firstname;
    }

    public void setLastName(String lastname) {
        this.lastname = lastname;
    }
}

# How To Exclude Some Fields by annotating them with `@ToString.Exclude`

Now incase you want to exclude some fields from being returned in the string representation of our object, you can annotate them with @ToString.Exclude.

Let's create a Person class to demonstrate this. Full code here


//demo4
package com.stevenmwesigwa.tostring.demo4;

import lombok.ToString;

@ToString
public class Person {

    private String firstname;
    @ToString.Exclude
    private String lastname;

    public void setFirstName(String firstname) {
        this.firstname = firstname;
    }

    public void setLastName(String lastname) {
        this.lastname = lastname;
    }
}

Note how we excluded the lastname field from showing up.

# How To use `DoNotUseGetters` Configuration Key With @ToString annotation

By default, lombok.toString.doNotUseGetters configuration key has it's value as false . Meaning if we explicitly defined a getter method for a non-static field to be included, it is called instead of using a direct reference of the field.

Setting lombok.toString.doNotUseGetters to true does the opposite.

Let's create a Person class to demonstrate this. Full code here


//demo5
package com.stevenmwesigwa.tostring.demo5;

import lombok.ToString;

@ToString(doNotUseGetters = true)
public class Person {

    private String firstname;
    private String lastname;

    public void setFirstName(String firstname) {
        this.firstname = firstname;
    }

    public void setLastName(String lastname) {
        this.lastname = lastname;
    }

    public String getFirstname() {
        return "FIRST: " + firstname;
    }

    public String getLastname() {
        return "LAST: " + lastname;
    }

}

Now if you're keen enough, you will notice that because we set lombok.toString.doNotUseGetters to true, are direct field reference was used instead of our custom getter methods.

Our custom getter methods have "FIRST: " and "LAST: " text prepended to field values but this wasn't returned.

I hope you find this helpful.

Ok, this should be enough to get you comfortable with @ToString lombok annotation.

Don't hesitate to leave a comment. Your feedback is greatly appreciated.

About The Author

Steven Mwesigwa

Software Engineer at Vogue Book Consultancy Services Ltd

Steve is currently a software developer at Vogue Book Consultancy Services Ltd and a technology author. He holds a Dip. in civil engineering from Kyambogo University. He founded...

@ToString

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