Java 鏈式編程 和 lombok 實現鏈式編程

文章目錄

• 一、鏈式編程定義
• 二、jdk中 StringBuffer 源碼
• 三、按照上面的方法寫一個例子
• 四、`lombok` 鏈式編程
• 五、`lombok` 實現靜態的鏈式編程
• 六、自定義 builder模式的鏈式Bean
• 七、`lombok` 實現 builder模式的鏈式bean
• 八、 更多其他Lombok注解的使用
• 參考

一、鏈式編程定義

鏈式編程的原理就是返回一個this對象，就是返回本身，達到鏈式效果。

二、jdk中 StringBuffer 源碼

我們經常用的 StringBuffer 就是 實現了鏈式的寫法。

StringBuffer builder = new StringBuffer();
builder.append("blake").append("bob").append("alice").append("linese").append("eve");

是不是很方便呢!

怎么實現呢，其實就是在設置的 返回當前的對象 。

源碼如下：

@Override
public StringBuilder append(String str) {
    super.append(str);
    return this;
}

三、按照上面的方法寫一個例子

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;
	}
}

測試：

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 鏈式編程

其實，lombok 已經提供該 style，我們把這個bean 改成 lombok 實現只需要加上一個 @Accessors(chain = true) 即可。

@Accessors(chain = true)
@Getter
@Setter
public class StudentBean {

	private String name;	
	private int age;
	
}

上面代碼編譯之后：

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 實現靜態的鏈式編程

寫StudentBean這個bean的時候，會有一些必輸字段，比如StudentBean中的name字段，一般處理的方式是將name字段包裝成一個構造方法，只有傳入name這樣的構造方法，才能創建一個StudentBean對象。

使用 lombok 將更改成如下寫法： @RequiredArgsConstructor 和 @NonNull

@Accessors(chain = true)
@Getter
@Setter
@RequiredArgsConstructor(staticName = "of")
public class StudentBean {

	@NonNull
	private String name;
	
	private int age;
}

上面代碼編譯之后：

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);
    }
}

測試方法：

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());
	}
}

這樣不僅實現了鏈式編程，還實現了靜態創建。

六、自定義 builder模式的鏈式Bean

build模式實現原理為在bean里面創建一個 靜態builder方法 和一個 靜態內部Builder類 ，通過調用靜態builder方法來創建 Builder類，然后通過 builder類 中的 build方法直接創建一個Bean，具體如下：

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;
		}
	}
}

測試方法：

StudentBean studentBean = StudentBean.builder().name("zhangsan").age(11).build();

七、lombok 實現 builder模式的鏈式bean

這樣就實現了一個builder模式的鏈式bean。其實用lombok就一個注解的事情，調用與上面同樣

@Builder
public class StudentBean {
	private String name;
	
	private int age;
}

上面代碼編譯之后：

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 + ")";
        }
    }
}

可以發現添加了 @Builder 注解之后，自動生成了靜態builder方法 和一個 靜態內部Builder類，並沒有生成 get、set 方法，我們在上面例子中加入 @Data和 @Accessors(chain = true)注解：

@Builder
@Data
@Accessors(chain = true)
public class StudentBean {
    private String name;

    private int age;
}

上面代碼編譯之后：

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 + ")";
        }
    }
}

最終生成類如上面一樣，屬性的 get、set 方法有了，並且支持鏈式調用，而且還是builder模式。

八、 更多其他Lombok注解的使用

• lombok注解介紹
• 使用Lombok簡化java代碼的編寫

參考

https://blog.csdn.net/xiaojin21cen/article/details/83478929