Java 自定义注解查找方法

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，然后写方法 return getter 或 setter 方法这个变量的注释设置 id;

例如，我做了类似的东西，但只针对方法，所以我需要为 setter 和 getter 方法提供两个注释，或者向一个注释添加更多参数。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）？

我设法做到的：

注解class:

    public @interface FieldRawValue {

    String value() default "";
}

模型 class，具有 getters 和 setters（带有 getters 的注释）：

public class PajamuModel 扩展了 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;
}...

方法，其中 returns 数据按注释值：

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，未测试 get(String fieldName) 方法，但我希望它有效。

那么可不可以在变量上设置注解，然后在需要的时候再找set或者get方法呢？

Answer 1

我不确定为什么要复制字段名并将其放在注释中，但这是解决方案（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+用途：

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
    }

}

Java 自定义注解查找方法

Java custom annotation to find methods

java

annotations