Java 链式编程 和 lombok 实现链式编程
文章目录
一、链式编程定义
链式编程的原理就是返回一个this对象，就是返回本身，达到链式效果。
二、jdk中 StringBuffer 源码
我们经常用的 StringBuffer 就是 实现了链式的写法。
StringBuffer builder = new StringBuffer();
builder.append("blake").append("bob").append("alice").append("linese").append("eve");
是不是很方便呢!
怎么实现呢，其实就是在设置的 返回当前的对象 。
源码如下：
@Override
public StringBuilder append(String str) {
super.append(str);
return this;
}
三、按照上面的方法写一个例子
public class StudentBean {
private String name;
private int age;
public String getName() {
return name;
}
public StudentBean setName(String name) {
this.name = name;
return this;
}
public int getAge() {
return age;
}
public StudentBean setAge(int age) {
this.age = age;
return this;
}
}
测试：
public class Main {
public static void main(String[] args) {
StudentBean studentBean = new StudentBean().setAge(22).setName("ly");
System.out.println(studentBean.getAge());
System.out.println(studentBean.getName());
}
}
四、lombok 链式编程
其实，lombok 已经提供该 style，我们把这个bean 改成 lombok 实现只需要加上一个 @Accessors(chain = true) 即可。
@Accessors(chain = true)
@Getter
@Setter
public class StudentBean {
private String name;
private int age;
}
上面代码编译之后：
public class StudentBean {
private String name;
private int age;
public StudentBean() {
}
public String getName() {
return this.name;
}
public int getAge() {
return this.age;
}
public StudentBean setName(String name) {
this.name = name;
return this;
}
public StudentBean setAge(int age) {
this.age = age;
return this;
}
}
五、lombok 实现静态的链式编程
写StudentBean这个bean的时候，会有一些必输字段，比如StudentBean中的name字段，一般处理的方式是将name字段包装成一个构造方法，只有传入name这样的构造方法，才能创建一个StudentBean对象。
使用 lombok 将更改成如下写法： @RequiredArgsConstructor 和 @NonNull
@Accessors(chain = true)
@Getter
@Setter
@RequiredArgsConstructor(staticName = "of")
public class StudentBean {
@NonNull
private String name;
private int age;
}
上面代码编译之后：
public class StudentBean {
@NonNull
private String name;
private int age;
@NonNull
public String getName() {
return this.name;
}
public int getAge() {
return this.age;
}
public StudentBean setName(@NonNull String name) {
if (name == null) {
throw new NullPointerException("name");
} else {
this.name = name;
return this;
}
}
public StudentBean setAge(int age) {
this.age = age;
return this;
}
private StudentBean(@NonNull String name) {
if (name == null) {
throw new NullPointerException("name");
} else {
this.name = name;
}
}
public static StudentBean of(@NonNull String name) {
return new StudentBean(name);
}
}
测试方法：
public class Main {
public static void main(String[] args) {
StudentBean studentBean = StudentBean.of("zhangsan").setAge(22);
System.out.println(studentBean.getAge());
System.out.println(studentBean.getName());
}
}
这样不仅实现了链式编程，还实现了静态创建。
六、自定义 builder模式的链式Bean
build模式实现原理为在bean里面创建一个 静态builder方法 和一个 静态内部Builder类 ，通过调用静态builder方法来创建 Builder类，然后通过 builder类 中的 build方法直接创建一个Bean，具体如下：
public class StudentBean {
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public static Builder builder() {
return new Builder();
}
public static class Builder{
private String name;
private int age;
public Builder name(String name) {
this.name = name;
return this;
}
public Builder age(int age) {
this.age = age;
return this;
}
public StudentBean build() {
StudentBean studentBean = new StudentBean();
studentBean.setName(name);
studentBean.setAge(age);
return studentBean;
}
}
}
测试方法：
StudentBean studentBean = StudentBean.builder().name("zhangsan").age(11).build();
七、lombok 实现 builder模式的链式bean
这样就实现了一个builder模式的链式bean。其实用lombok就一个注解的事情，调用与上面同样
@Builder
public class StudentBean {
private String name;
private int age;
}
上面代码编译之后：
public class StudentBean {
private String name;
private int age;
StudentBean(String name, int age) {
this.name = name;
this.age = age;
}
public static StudentBean.StudentBeanBuilder builder() {
return new StudentBean.StudentBeanBuilder();
}
public static class StudentBeanBuilder {
private String name;
private int age;
StudentBeanBuilder() {
}
public StudentBean.StudentBeanBuilder name(String name) {
this.name = name;
return this;
}
public StudentBean.StudentBeanBuilder age(int age) {
this.age = age;
return this;
}
public StudentBean build() {
return new StudentBean(this.name, this.age);
}
public String toString() {
return "StudentBean.StudentBeanBuilder(name=" + this.name + ", age=" + this.age + ")";
}
}
}
可以发现添加了 @Builder 注解之后，自动生成了静态builder方法 和一个 静态内部Builder类，并没有生成 get、set 方法，我们在上面例子中加入 @Data和 @Accessors(chain = true)注解：
@Builder
@Data
@Accessors(chain = true)
public class StudentBean {
private String name;
private int age;
}
上面代码编译之后：
public class StudentBean {
private String name;
private int age;
StudentBean(String name, int age) {
this.name = name;
this.age = age;
}
public static StudentBean.StudentBeanBuilder builder() {
return new StudentBean.StudentBeanBuilder();
}
private StudentBean() {
}
public String getName() {
return this.name;
}
public int getAge() {
return this.age;
}
public StudentBean setName(String name) {
this.name = name;
return this;
}
public StudentBean setAge(int age) {
this.age = age;
return this;
}
public boolean equals(Object o) {
if (o == this) {
return true;
} else if (!(o instanceof StudentBean)) {
return false;
} else {
StudentBean other = (StudentBean)o;
if (!other.canEqual(this)) {
return false;
} else {
Object this$name = this.getName();
Object other$name = other.getName();
if (this$name == null) {
if (other$name == null) {
return this.getAge() == other.getAge();
}
} else if (this$name.equals(other$name)) {
return this.getAge() == other.getAge();
}
return false;
}
}
}
protected boolean canEqual(Object other) {
return other instanceof StudentBean;
}
public int hashCode() {
int PRIME = true;
int result = 1;
Object $name = this.getName();
int result = result * 59 + ($name == null ? 43 : $name.hashCode());
result = result * 59 + this.getAge();
return result;
}
public String toString() {
return "StudentBean(name=" + this.getName() + ", age=" + this.getAge() + ")";
}
public static class StudentBeanBuilder {
private String name;
private int age;
StudentBeanBuilder() {
}
public StudentBean.StudentBeanBuilder name(String name) {
this.name = name;
return this;
}
public StudentBean.StudentBeanBuilder age(int age) {
this.age = age;
return this;
}
public StudentBean build() {
return new StudentBean(this.name, this.age);
}
public String toString() {
return "StudentBean.StudentBeanBuilder(name=" + this.name + ", age=" + this.age + ")";
}
}
}
最终生成类如上面一样，属性的 get、set 方法有了，并且支持链式调用，而且还是builder模式。
八、 更多其他Lombok注解的使用
参考
