lombok的@Builder实际是建造者模式的一个变种，所以在创建复杂对象时常使用
这里对lombok的@Builder和@Data组合的使用示例
import lombok.Builder;
import lombok.Data; @Data
@Builder
public class People {
private String name;
private String sex;
private int age;
}
使用了@Bulider和@Data注解后，就可以使用链式风格优雅地创建对象
public class TestLombok {
@Test
public void testBuilderAnnotation(){
People luoTianyan = People.builder()
.sex("female")
.age(23)
.name("LuoTianyan")
.build();
System.out.println(luoTianyan.toString());
//People(name=LuoTianyan, sex=female, age=23)
People people = new People("LuoTianyan","female",23);
System.out.println(luoTianyan.equals(people));
//true
}
}
class People加上了@Builder和@Data注解后，多了一个静态内部类PeopleBuilder，People调用静态方法builder生成PeopleBuilder对象，PeopleBuilder对象可以使用".属性名(属性值)"的方式进行属性设置，再调用build()方法就生成了People对象，并且如果两个People对象的属性如果相同，就会认为这两个对象相等，即重写了hashCode和equls方法。
这里就直接在Intellij IDEA下，查看反编译的文件People.class；
可以看到，生成的有：
- Getter和Setter方法；
- 访问类型是private无参构造方法，访问类型为default的全部参数的构造方法；
- 重写hashCode、equals、toString方法，则People可以做为Map的key；
- 访问类型为public的静态方法builder，返回的是People.PeopleBuilder对象，非单例；
- 访问类型为public的静态内部类PeopleBuilder，该类主要有build方法，返回类型是People；
- 最后还有个canEqual方法，判断是否与People同类型。
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
// public class People {
private String name;
private String sex;
private int age; People(String name, String sex, int age) {
this.name = name;
this.sex = sex;
this.age = age;
} public static People.PeopleBuilder builder() {
return new People.PeopleBuilder();
} private People() {
} public String getName() {
return this.name;
} public String getSex() {
return this.sex;
} public int getAge() {
return this.age;
} public void setName(String name) {
this.name = name;
} public void setSex(String sex) {
this.sex = sex;
} public void setAge(int age) {
this.age = age;
} public boolean equals(Object o) {
if (o == this) {
return true;
} else if (!(o instanceof People)) {
return false;
} else {
People other = (People)o;
if (!other.canEqual(this)) {
return false;
} else {
label39: {
Object this$name = this.getName();
Object other$name = other.getName();
if (this$name == null) {
if (other$name == null) {
break label39;
}
} else if (this$name.equals(other$name)) {
break label39;
} return false;
} Object this$sex = this.getSex();
Object other$sex = other.getSex();
if (this$sex == null) {
if (other$sex != null) {
return false;
}
} else if (!this$sex.equals(other$sex)) {
return false;
} if (this.getAge() != other.getAge()) {
return false;
} else {
return true;
}
}
}
} protected boolean canEqual(Object other) {
return other instanceof People;
} public int hashCode() {
int PRIME = true;
int result = 1;
Object $name = this.getName();
int result = result * 59 + ($name == null ? 43 : $name.hashCode());
Object $sex = this.getSex();
result = result * 59 + ($sex == null ? 43 : $sex.hashCode());
result = result * 59 + this.getAge();
return result;
} public String toString() {
return "People(name=" + this.getName() + ", sex=" + this.getSex() + ", age=" + this.getAge() + ")";
} public static class PeopleBuilder {
private String name;
private String sex;
private int age; PeopleBuilder() {
} public People.PeopleBuilder name(String name) {
this.name = name;
return this;
} public People.PeopleBuilder sex(String sex) {
this.sex = sex;
return this;
} public People.PeopleBuilder age(int age) {
this.age = age;
return this;
} public People build() {
return new People(this.name, this.sex, this.age);
} public String toString() {
return "People.PeopleBuilder(name=" + this.name + ", sex=" + this.sex + ", age=" + this.age + ")";
}
}
}
自从Java 6起，Javac就支持“JSR 269 Pluggable Annotation Processing API”规范，只要程序实现了该API，就能在javac运行的时候得到调用。
Lombok就是一个实现了"JSR 269 API"的程序。在使用javac的过程中，它产生作用的具体流程如下：
Javac对源代码进行分析，生成一棵抽象语法树(AST)
Javac编译过程中调用实现了JSR 269的Lombok程序
此时Lombok就对第一步骤得到的AST进行处理，找到Lombok注解所在类对应的语法树(AST)，然后修改该语法树(AST)，增加Lombok注解定义的相应树节点
Javac使用修改后的抽象语法树(AST)生成字节码文件