注解在数据初始化中的应用

Feb 10 2020

Java 中的注解在进行框架设计中非常有用，比如 SpringBoot，SpringMVC 框架中，今天就针对注解在数据初始化中的场景进行演示

数据初始化

定义一个注解，用来给对象做初始化工作，同时再定义注入数据的代码，就可以重复地使用注解了

定义 Java bean 类

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class Person{
    private String name;
    private int age;
    private String gender;
    
    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 String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }
}

定义注解

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@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface injectData {
    String name();

    int age();

    String gender();
}

定义注解数据注入方法，这里放到一个父类中

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class Base{
    protected Person person;

    public Base(){
        try {
            injectAnno();
        } catch (NoSuchFieldException | IllegalAccessException | InstantiationException e) {
            e.printStackTrace();
        }
    }

    protected void injectAnno() throws NoSuchFieldException, IllegalAccessException, InstantiationException {
        Field field = this.getClass().getDeclaredField("person");
        Person person = (Person) field.getType().newInstance();
        // 判断成员变量是否包含该注解
        if (field.isAnnotationPresent(InjectData.class)){
            // 获得这个注解对象
            InjectData injectData = field.getAnnotation(InjectData.class);
            person.setAge(injectData.age());
            person.setGender(injectData.gender());
            person.setName(injectData.name());
            setPerson(person);
        }
    }
    
    public Person getPerson() {
        return person;
    }

    public void setPerson(Person person) {
        this.person = person;
    }
}

使用注解

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class A extends Base{
    @InjectData(name = "idea", age = 5, gender = "male")
    protected Person person;
}

class B extends Base{
    @InjectData(name = "java", age = 20, gender = "female")
    protected Person person;
}

执行代码

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A a = new A();
B b = new B();
Person aa = a.getPerson();
Person bb = b.getPerson();
System.out.println(String.format("A: name:%s, age:%s, gender:%s", aa.getName(), aa.getAge(), aa.getGender()));
System.out.println(String.format("B: name:%s, age:%s, gender:%s", bb.getName(), bb.getAge(), bb.getGender()));

A: name:idea, age:5, gender:male
B: name:java, age:20, gender:female

使用注解来初始化的好处是让编写具体应用代码的过程更加简洁，更加关注于数据的注入过程，让代码可读性和可维护性更高