lombok basic annotation @Builder

The most complete lombok annotation details (updated from time to time with the version)

1. Annotation introduction

@Builder annotation to generate relatively slightly complex builder APIs

It acts on the class, turning it into the builder pattern
Can be called in chain form
The object generated by initializing the instance object cannot be changed, and can be assigned when creating the object.
If you need to modify it on the original basis, you can add the set method, and the final field does not require initialization.
It generates a constructor with full parameters

2. Introduction to attributes

@: Non-final fields can have default values
builderMethodName: Specify the method name for creating an internal static class, the default value is builder
buildMethodName: Specify the method name for creating entity class, the default value is build
builderClassName: Specify the internal static class name, the default value is "", and the default created class name is thisclassBuilder
toBuilder: Set to true to copy this object to generate a new object, which can be modified again, and the default is false
access: Set the access permission modifier of builderMethodName, default to public
There are PUBLIC, MODULE, PROTECTED, PACKAGE, and PRIVATE, among which MODULE is a new feature of Java 9.
setterPrefix: Set the prefix of the setter method, default to ""

3. Practical drills

@Builder(
	builderMethodName = "builder", buildMethodName = "build", builderClassName = "",
	toBuilder = true, access = AccessLevel.PUBLIC, setterPrefix = ""
)
public class Yifei {
	@
	private String name = "Liu Yifei";
	
	private String sex;
	
	private final Integer age = 18;	// Default can be initialized successfully if the final field is added or not.
	
	public static void main(String[] args) {
		Yifei yifei = Yifei.builder().build();	// If no Default is added, the output name result is null.
		/**
		  * Similar to copy, the name value has been modified, the age value is still the same
		  * If toBuilder = false, there is no toBuilder method
		  */
		yifei = yifei.toBuilder().name("Liu Yifei").build();
	}
}

We often use generics in our daily development, and @Builder also supports specified generic construction

@Builder
public class Yifei<T> {
	public void yiyang(Yifei<T> yi) {
		yi = Yifei.<T>builder().builder();
	}
}

@Builder will generate a full parameter construction method, so there is no parameterless construction method, but when we encounter a method without parameterless construction method, problems will occur. At this time, handwriting or adding@NoArgsConstructorThere will be errors, two solutions

1. Add@AllArgsConstructor

@Builder
@AllArgsConstructor
public class Yifei {
	public Yifei() {
		/**
		  * Handwriting or @NoArgsConstructor will invalidate the full parameter constructor generated by @Builder
		  * At this time, an error was reported, and you can add @AllArgsConstructor or write a full parameter constructor by hand.
		  */
	}
}

2. Use@Tolerateannotation

4. Attribute expansion

lombok basic annotation @

5. What is done inside @Builder

Create an internal static class called ThisClassBuilder with the same properties as the entity class (called the builder)
In the builder: for all properties in the target class and uninitialized final fields, corresponding properties are created in the builder.
In the builder: Create a default constructor without parameters
In the builder: Each parameter in the entity class will create a setter-like method, with the same method name as the parameter name. And the return value is the builder itself (for chained calls)
In the builder: a build method will be created, the build method will be called, and the entity object will be created based on the set value
In the builder: a toString method is generated
In entity class: a builder method is created, and its purpose is to create a builder

@Builder
public class User {
    private String username;
    private String password;
}

After compilation

public class User {
    private String username;
    private String password;
    
    User(String username, String password) {
        this.username = username;
        this.password = password;
    }
    
    public static User.UserBuilder builder() {
        return new User.UserBuilder();
    }
	
    public static class UserBuilder {
        private String username;
        private String password;
        
        UserBuilder() {}
		
        public User.UserBuilder username(String username) {
            this.username = username;
            return this;
        }
        
        public User.UserBuilder password(String password) {
            this.password = password;
            return this;
        }
        
        public User build() {
            return new User(this.username, this.password);
        }
        
		public String toString() {
            return "(username=" + this.username + ", password=" + this.password + ")";
        }
    }
}