1、建造者模式簡介：Builder 使用創(chuàng)建者模式又叫建造者模式。簡單來說，就是一步步創(chuàng)建一個對象，它對用戶屏蔽了里面構建的細節(jié)，但卻可以精細地控制對象的構造過程。

2、注解類Builder.java注釋：

* 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.

在企業(yè)開發(fā)中，一般在領域對象實體上標注@Builder，其作用就相當于@AllArgsConstructor(access = AccessLevel.PRIVATE),@Builder一般與@Getter結合使用。

3、實戰(zhàn)① 編寫測試實體類。

import lombok.Builder;import lombok.Getter;@Builder//@Getterpublic class Person { private String name; private String id; private String phoneNumeber;}

② 編寫測試類。

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編譯并執(zhí)行的結果為：Person.PersonBuilder(name=asdd, id=1123, phoneNumeber=11111)

④ 編譯后的字節(jié)碼分析：

//// 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：生成一個全屬性的構造器生成了一個返回靜態(tài)內部類PersonBuilder對象的方法生成了一個靜態(tài)內部類PersonBuilder，這個靜態(tài)內部類包含Person類的三個屬性，無參構造器，三個方法名為屬性名的方法，返回Person對象的build方法，輸出靜態(tài)內部類三個屬性的toString()方法。

⑤ 建造者使用過程：

Person.PersonBuilder builder = Person.builder(); builder.phoneNumeber('11111').id('1123').name('asdd').build(); System.out.println(builder);

先實例化內部類對象并返回，然后為調用內部類的方法為內部類的屬性賦值，build()方法就是將內部類PersonBuilder的屬性值傳入Person構造器中，實例化Person對象。

以上即為對于@Builder的簡單使用。

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