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How to make good use of builder mode

2022-08-04 20:25:00 【51CTO】

How to make good use of builder mode_建造者

介绍

I wrote a project some time ago,An attribute of a class is called more than one.Just started writing a bunch directlyset代码,后来setThe code is just too much,真心看不下去了,Refactored a bit using the builder pattern,嗯,看起来舒服多了.Basically, the builder pattern is used in many frameworks,每个JavaProgrammers must have used the builder pattern too,You just don't realize that this is the builder pattern.

就像你用Collections.sort(List,Comparator)和Arrays.sort(Object[],Comparator)This is a typical implementation of the strategy pattern,Different effects are achieved by passing in different comparators.

改造过程

First let me demonstrate the process of my transformation,用了Lombok插件,不会的可以百度一下.

原来的实现

       
       @Data
       
       public 
       
       class 
       
       Student {
       
       private 
       
       String 
       
       name;
       
       private 
       
       int 
       
       age;
       
       private 
       
       int 
       
       gender;
       
}
      
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测试类

       
       public 
       
       class 
       
       Test {
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args) {
       
       Student 
       
       student 
       
       = 
       
       new 
       
       Student();
       
       student.
       
       setName(
       
       "小明");
       
       student.
       
       setAge(
       
       10);
       
       student.
       
       setGender(
       
       1);
       
       // Student(name=小明, age=10, gender=1)
       
       System.
       
       out.
       
       println(
       
       student);
       
    }
       
}
      
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后来的实现

       
       @Data
       
       @Builder
       
       public 
       
       class 
       
       Student {
       
       private 
       
       String 
       
       name;
       
       private 
       
       int 
       
       age;
       
       private 
       
       int 
       
       gender;
       
}
      
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测试类

       
       public 
       
       class 
       
       Test {
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args) {
       
       Student 
       
       student 
       
       = 
       
       Student.
       
       builder().
       
       name(
       
       "小明")
       
                .
       
       age(
       
       10).
       
       gender(
       
       1).
       
       build();
       
       // Student(name=小明, age=10, gender=1)
       
       System.
       
       out.
       
       println(
       
       student);
       
    }
       
}
      
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全程链式调用,Know clearly what each field means,And also save the number of lines,not too cool.

How to write a builder pattern？

Look directly at the final compilation generatedclassThe contents of the decompiled file

       
       public 
       
       class 
       
       Student {
       
       private 
       
       String 
       
       name;
       
       private 
       
       int 
       
       age;
       
       private 
       
       int 
       
       gender;
       
       Student(
       
       String 
       
       name, 
       
       int 
       
       age, 
       
       int 
       
       gender) {
       
       this.
       
       name 
       
       = 
       
       name;
       
       this.
       
       age 
       
       = 
       
       age;
       
       this.
       
       gender 
       
       = 
       
       gender;
       
    }
       
       public 
       
       static 
       
       Student.
       
       StudentBuilder 
       
       builder() {
       
       return 
       
       new 
       
       Student.
       
       StudentBuilder();
       
    }
       
       // 省略get和set方法
       
       public 
       
       String 
       
       toString() {
       
       return 
       
       "Student(name=" 
       
       + 
       
       this.
       
       getName() 
       
       + 
       
       ", age=" 
       
       + 
       
       this.
       
       getAge() 
       
       + 
       
       ", gender=" 
       
       + 
       
       this.
       
       getGender() 
       
       + 
       
       ")";
       
    }
       
       public 
       
       static 
       
       class 
       
       StudentBuilder {
       
       private 
       
       String 
       
       name;
       
       private 
       
       int 
       
       age;
       
       private 
       
       int 
       
       gender;
       
       StudentBuilder() {
       
        }
       
       public 
       
       Student.
       
       StudentBuilder 
       
       name(
       
       String 
       
       name) {
       
       this.
       
       name 
       
       = 
       
       name;
       
       return 
       
       this;
       
        }
       
       public 
       
       Student.
       
       StudentBuilder 
       
       age(
       
       int 
       
       age) {
       
       this.
       
       age 
       
       = 
       
       age;
       
       return 
       
       this;
       
        }
       
       public 
       
       Student.
       
       StudentBuilder 
       
       gender(
       
       int 
       
       gender) {
       
       this.
       
       gender 
       
       = 
       
       gender;
       
       return 
       
       this;
       
        }
       
       public 
       
       Student 
       
       build() {
       
       return 
       
       new 
       
       Student(
       
       this.
       
       name, 
       
       this.
       
       age, 
       
       this.
       
       gender);
       
        }
       
    }
       
}
      
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I don't think I need to explain what this code means for you,That's two parts.

1.Generate builder class,Assign a value to the builder class
2.Use the builder class to generate the desired class

恭喜你,Already understand what the builder pattern is.

Lombok中@Builder注解的使用

if available in your projectLombok插件,You don't have to write your own builder class,直接用@Builder注解即可.如果不可以,Writing a builder class that mimics the above class is also [email protected] the following points to note.

There is no case of inheritance

上面已经演示了

There are cases of inheritance

1.对于父类,使用@AllArgsConstructor注解
2.对于子类,Manually write full-parameter constructors,Internally calls the parent class full parameter constructor,Used on subclass full-argument [email protected]注解

       
       @Data
       
       @AllArgsConstructor
       
       public 
       
       class 
       
       Person {
       
       private 
       
       int 
       
       weight;
       
       private 
       
       int 
       
       height;
       
}
      
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       @Data
       
       @ToString(
       
       callSuper 
       
       = 
       
       true)
       
       public 
       
       class 
       
       Student 
       
       extends 
       
       Person {
       
       private 
       
       String 
       
       schoolName;
       
       private 
       
       String 
       
       grade;
       
       @Builder
       
       public 
       
       Student(
       
       int 
       
       weight, 
       
       int 
       
       height, 
       
       String 
       
       schoolName, 
       
       String 
       
       grade) {
       
       super(
       
       weight, 
       
       height);
       
       this.
       
       schoolName 
       
       = 
       
       schoolName;
       
       this.
       
       grade 
       
       = 
       
       grade;
       
    }
       
       public 
       
       static 
       
       void 
       
       main(
       
       String[] 
       
       args) {
       
       Student 
       
       student 
       
       = 
       
       Student.
       
       builder().
       
       schoolName(
       
       "清华附小").
       
       grade(
       
       "二年级")
       
                .
       
       weight(
       
       10).
       
       height(
       
       10).
       
       build();
       
       // Student(super=Person(weight=10, height=10), schoolName=清华附小, grade=二年级)
       
       System.
       
       out.
       
       println(
       
       student.
       
       toString());
       
    }
       
}
      
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在框架中的应用

基本上所有的JavaFrameworks use the builder pattern,Because chained assignment is really cool.我GoogleA little bit of code using the builder pattern,方便大家理解

Guava Cache框架

       
       Cache
       
       <
       
       String,
       
       String
       
       > 
       
       cache 
       
       = 
       
       CacheBuilder.
       
       newBuilder()
       
    .
       
       maximumSize(
       
       2)
       
    .
       
       expireAfterWrite(
       
       3,
       
       TimeUnit.
       
       SECONDS)
       
    .
       
       build();
      
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