【学习笔记】lombok的@Builder注解

首先需要了解下Builder模式：

定义一个User类：

public class User {
    

  private String firstName;
  private String lastName;

  User(String firstName, String lastName) {
    
    this.firstName = firstName;
    this.lastName = lastName;
  }

  public static Builder builder() {
    
      return new Builder();
  }

  public static class Builder {
    

    String firstName;
    String lastName;

    Builder firstName(String value) {
    
        this.firstName = value;
        return this;
    }

    Builder lastName(String value) {
    
        this.lastName = value;
        return this;
    }

    public User build() {
    
        return new User(firstName, lastName);
    }
  }
}

则可以通过链式调用的方式为User的属性赋值：

User user = User.builder()
      .firstName("san")
      .lastName("zhang")
      .build();

之所以能够链式调用是因为User.Builder类中的firstName()和lastName()方法返回的都是Builder对象。

而@Builder注解的使用可以大大简化代码：

@Builder
public class User {
    
    private String firstName;
   private String lastName;
}

在使用时和之前一样：

User user = User.Build()
      .firstName("san")
      .lastName("zhang")
      .build();