@Builder注解如何在Java中使用-创新互联
@Builder注解如何在Java中使用？相信很多没有经验的人对此束手无策，为此本文总结了问题出现的原因和解决方法，通过这篇文章希望你能解决这个问题。
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}.
*
* 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。
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