用于查找方法的 Java 自定义注解

Question

我想创建注释（我可以为它设置某种id），我可以把它放在变量上，并编写方法，通过注释设置的id返回这个变量的getter或setter方法；

作为示例，我做了类似的事情，但仅用于方法，所以我需要两个注解用于 setter 和 getter 方法，或者向一个注解添加更多参数。也许可以为变量创建一个注释，然后找到我需要的方法（setter 或 getter）？

我做了什么：

注解类：

    public @interface FieldRawValue {

    String value() default "";
}

带有 getter 和 setter 的模型类（带有 getter 注释）：

公共类 PajamuModel 扩展 AbstractModel{

private String id;
private String pajamuType;
private String pajamuSource;
private Date pajamuData;
private double pajamuSuma;
private String valiuta;
private String note;

@FieldRawValue(value = "pajamuType")
public String getPajamuType() {
    return pajamuType;
}

public void setPajamuType(String pajamuType) {
    this.pajamuType = pajamuType;
}

@FieldRawValue(value = "pajamuSource")
public String getPajamuSource() {
    return pajamuSource;
}

public void setPajamuSource(String pajamuSource) {
    this.pajamuSource = pajamuSource;
}

@FieldRawValue(value = "pajamuData")
public Date getPajamuData() {
    return pajamuData;
}...

通过注解值返回数据的方法：

public class AbstractModel {

public Object get(String fieldName) {
    Class<? extends AbstractModel> obj = this.getClass();

    for (Method method : obj.getDeclaredMethods()) {
        if (method.isAnnotationPresent(FieldRawValue.class)) {
            FieldRawValue annotation = method
                    .getAnnotation(FieldRawValue.class);
            if (annotation.value().equals(fieldName)) {
                try {
                    return method.invoke(obj);
                } catch (IllegalAccessException | IllegalArgumentException
                        | InvocationTargetException e) {
                    e.printStackTrace();
                    return null;
                }
            }
        }
    }

    return null;
}

顺便说一句，没有测试get(String fieldName) 方法，但我希望它可以工作。

那么是否可以在变量上设置注释，然后在需要时找到 set 或 get 方法？

Answer 1

我不确定为什么要复制字段名并将其放在注释中，但是这里是解决方案（需要 Java8）：

public class AbstractModel {

    public Object get(String fieldName) throws InvocationTargetException, IllegalAccessException {
        FieldRawValue fieldRawValueAnnotation = validateExistsAndGetFieldRawValueAnnotation(fieldName);

        String fieldRawValueString = fieldRawValueAnnotation.value();

        Optional<Method> getterMethodOptional = Stream.of(getClass().getMethods())
                .filter(method1 -> method1.getName().equalsIgnoreCase("get" + fieldRawValueString))
                .findFirst();

        return getterMethodOptional
                .orElseThrow(() -> new RuntimeException("No getter found for @FieldRawValue with value: " + fieldRawValueString))
                .invoke(this);
    }

    public Object set(String fieldName, Object value) throws InvocationTargetException, IllegalAccessException {
        FieldRawValue fieldRawValueAnnotation = validateExistsAndGetFieldRawValueAnnotation(fieldName);

        String fieldRawValueString = fieldRawValueAnnotation.value();

        Optional<Method> getterMethodOptional = Stream.of(getClass().getMethods())
                .filter(method1 -> method1.getName().equalsIgnoreCase("set" + fieldRawValueString))
                .findFirst();

        return getterMethodOptional
                .orElseThrow(() -> new RuntimeException("No setter found for @FieldRawValue with value: " + fieldRawValueString))
                .invoke(this, value);
    }

    private FieldRawValue validateExistsAndGetFieldRawValueAnnotation(String fieldName) {
        Class<? extends AbstractModel> obj = this.getClass();

        FieldRawValue fieldRawValueAnnotation = null;
        try {
            fieldRawValueAnnotation = obj.getDeclaredField(fieldName).getAnnotation(FieldRawValue.class);
        } catch (NoSuchFieldException e) {
            new RuntimeException("Field not found: " + fieldName);
        }

        if(fieldRawValueAnnotation == null){
            throw new RuntimeException("FieldRawValue annotation not found for a field: " + fieldName);
        }
        return fieldRawValueAnnotation;
    }

型号+用法：

public class TestModel extends AbstractModel{

    @FieldRawValue("test2")
    private String test;

    public String getTest2() {
        return test;
    }

    public void setTest2(String test) {
        this.test = test;
    }

    public static void main(String[] args) throws InvocationTargetException, IllegalAccessException {
        TestModel testModel = new TestModel();

        Object tst = testModel.get("test"); //== null
        testModel.set("test", "newVal"); //sets new value
        testModel.get("test"); //== "newVal
    }

}