Builder设计模式

Java代码实现

• Step_1：在类中创建一个静态内部类Builder，Builder类中要包含所在类的全部属性;

  public static class Builder{
      private String id;
      private String name;
  }
  

---

• Step_2: Builder类要为每一个属性创建赋值方法，并返回当前对象(返回对象为Builder)；

  public static class BUilder{
      
      ...
          
     public Builder id(String id){
         this.id = id;
         return this;
     }
     public Builder name(String name){
         this.name = name;
         return this;
     }  
  }
  

---

• Step_3: Builder类中创建build方法，返回Person对象并赋值。有两种赋值方式；

  • 方式一：

    • return new 所在类全参构造器(this.属性，this.属性...);

      该方式需要所在类有一个全参构造器；

  • 方式二：

    • return new 所在类构造器（this）;

      需要在所在类中创建一个参数为Builder的构造器；

      eg:

      public 所在类类名(Builder builder){

      ​ this.id = builder.id;

      ​ this.name = builder.name;

      ​ ...

      }

  public static class BUilder{
      
      ...
          
     public Student build(){
        return new Student(this);
     }
  }
  

---

• Step_4: 在所在类中，创建静态builder方法，返回Builder对象。

  public static Builder builder(){
          return new Builder();
      }
  
  
  public static class BUilder{
      
      ...
          
     public Student build(){
        return new Student(this);
     }
  }
  

---

完整代码：

public class Student{

    private String id;
    private String name;

    public Student(){};


    public Student(Builder builder){
        this.id = builder.id;
        this.name = builder.name;
    }

    public static class Builder{
        private String id;
        private String name;

        public Builder id(String id){
            this.id = id;
            return this;
        }
        public Builder name(String name){
            this.name = name;
            return this;
        }

        public Student build(){
            return new Student(this);
        }
    }

    public static Builder builder(){
        return new Builder();
    }
    @Override
    public String toString() {
        return "Student{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                '}';
    }
}

---

如何使用：

@Test
public void builderStudentTest(){

    Student student = Student.builder()
              .id("0000")
              .name("王小明")
              .build();

    System.out.println(student);
}

Lombok实现

代码实现：

@Builder
@ToString
public class Employee{
    private String id;
    private String name;
    private Integer age;
    private String phone;
    private String address;
}

---

使用方式

@Test
    public void builderEmployeeTest(){
        Employee employee = Employee.builder()
                .id("0000")
                .name("Tom")
                .age(20)
                .phone("12344445555")
                .address("America")
                .build();
        System.out.println(employee);
    }

​