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//@Getterpublic 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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