Java中lombok的@Builder注解的解析与简单使用详解

lombok中@builder用法

1、建造者模式简介：builder 使用创建者模式又叫建造者模式。简单来说，就是一步步创建一个对象，它对用户屏蔽了里面构建的细节，但却可以精细地控制对象的构造过程。

2、注解类builder.java注释：

* the builder annotation creates a so-called 'builder' aspect to the class that is annotated or the class
 * that contains a member which is annotated with {@code @builder}.
 * <p>
 * if a member is annotated, it must be either a constructor or a method. if a class is annotated,
 * then a private constructor is generated with all fields as arguments
 * (as if {@code @allargsconstructor(access = accesslevel.private)} is present
 * on the class), and it is as if this constructor has been annotated with {@code @builder} instead.
 * note that this constructor is only generated if you haven't written any constructors and also haven't
 * added any explicit {@code @xargsconstructor} annotations. in those cases, lombok will assume an all-args
 * constructor is present and generate code that uses it; this means you'd get a compiler error if this
 * constructor is not present.

在企业开发中，一般在领域对象实体上标注@builder，其作用就相当于@allargsconstructor(access = accesslevel.private),@builder一般与@getter结合使用。

3、实战
① 编写测试实体类。

import lombok.builder;
import lombok.getter;

@builder
//@getter
public class person {
  private string name;

  private string id;

  private string phonenumeber;
}

② 编写测试类。

public class test {
  public static void main(string[] args) {


    person.personbuilder builder = person.builder();
    builder.phonenumeber("11111")
        .id("1123")
        .name("asdd").build();
    system.out.println(builder);


  }
}

③编译并执行的结果为：
person.personbuilder(name=asdd, id=1123, phonenumeber=11111)

④ 编译后的字节码分析：

//
// source code recreated from a .class file by intellij idea
// (powered by fernflower decompiler)
//

package com.atyunniao;

public class person {
  private string name;
  private string id;
  private string phonenumeber;

  person(string name, string id, string phonenumeber) {
    this.name = name;
    this.id = id;
    this.phonenumeber = phonenumeber;
  }

  public static person.personbuilder builder() {
    return new person.personbuilder();
  }

  public string getname() {
    return this.name;
  }

  public string getid() {
    return this.id;
  }

  public string getphonenumeber() {
    return this.phonenumeber;
  }

  public static class personbuilder {
    private string name;
    private string id;
    private string phonenumeber;

    personbuilder() {
    }

    public person.personbuilder name(string name) {
      this.name = name;
      return this;
    }

    public person.personbuilder id(string id) {
      this.id = id;
      return this;
    }

    public person.personbuilder phonenumeber(string phonenumeber) {
      this.phonenumeber = phonenumeber;
      return this;
    }

    public person build() {
      return new person(this.name, this.id, this.phonenumeber);
    }

    public string tostring() {
      return "person.personbuilder(name=" + this.name + ", id=" + this.id + ", phonenumeber=" + this.phonenumeber + ")";
    }
  }
}

@builder的作用：
生成一个全属性的构造器
生成了一个返回静态内部类personbuilder对象的方法
生成了一个静态内部类personbuilder，这个静态内部类包含person类的三个属性，无参构造器，三个方法名为属性名的方法，返回person对象的build方法，输出静态内部类三个属性的tostring()方法。

⑤ 建造者使用过程：

 person.personbuilder builder = person.builder();
    builder.phonenumeber("11111")
        .id("1123")
        .name("asdd").build();
    system.out.println(builder);

先实例化内部类对象并返回，然后为调用内部类的方法为内部类的属性赋值，build()方法就是将内部类personbuilder的属性值传入person构造器中，实例化person对象。

以上即为对于@builder的简单使用。

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