Java 链式编程和 lombok 实现链式编程

以你之姓@ 2022-02-02 02:29 504阅读 0赞

### 文章目录 ###

*   *  一、链式编程定义
     *  二、jdk中 StringBuffer 源码
     *  三、按照上面的方法写一个例子
     *  四、\`lombok\` 链式编程
     *  五、\`lombok\` 实现静态的链式编程
     *  六、自定义 builder模式的链式Bean
     *  七、\`lombok\` 实现 builder模式的链式bean
     *  八、 更多其他Lombok注解的使用
     *  参考

## 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：

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 ##

*  [lombok注解介绍][lombok]
 *  [使用Lombok简化java代码的编写][Lombok_java]

> ## 参考 ##
> 
> [https://blog.csdn.net/xiaojin21cen/article/details/83478929][https_blog.csdn.net_xiaojin21cen_article_details_83478929]

[lombok]: https://blog.csdn.net/sunsfan/article/details/53542374
[Lombok_java]: https://blog.csdn.net/liuchuanhong1/article/details/71754167
[https_blog.csdn.net_xiaojin21cen_article_details_83478929]: https://blog.csdn.net/xiaojin21cen/article/details/83478929