技術標籤：lombokjavalombok後端

Lombok中@Builder用法

1、建造者模式簡介：Builder 使用建立者模式又叫建造者模式。簡單來說，就是一步步建立一個物件，它對使用者遮蔽了裡面構建的細節，但卻可以精細地控制物件的構造過程。

2、註解類Builder.java註釋：

* 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.

在企業開發中，一般在領域物件實體上標註@Builder，其作用就相當於@AllArgsConstructor(access = AccessLevel.PRIVATE),@Builder一般與@Getter結合使用。

3、實戰
① 編寫測試實體類。

import lombok.Builder;
import lombok.Getter;

@Builder
//@Getter
public 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編譯並執行的結果為：
Person.PersonBuilder(name=asdd, id=1123, phoneNumeber=11111)

④ 編譯後的位元組碼分析：

//
// 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內部類PersonBuilder物件的方法
生成了一個靜態內部類PersonBuilder，這個靜態內部類包含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物件的build方法，輸出靜態內部類三個屬性的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);

先例項化內部類物件並返回，然後為呼叫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，例項化Person物件。

以上即為對於@Builder的簡單使用。