Java 使用bytebuddy是否可以增强注释具有特定属性值的字段？

我试图使用bytebuddy来重新定义现有的类。我正在寻找用特定注释注释的字段。我已经用这样的代码弄明白了：

new ByteBuddy()
        .redefine(<some class>)
        .field(
            ElementMatchers.isAnnotatedWith(<some annotation>)
        )
        ...

new ByteBuddy()
        .redefine(<some class>)
        .field(
            ElementMatchers.isAnnotatedWith(<some annotation>)
                .havingAttribute(<some attribute>, "value")
        )

@Advice.OnMethodEnter(suppress = Throwable.class)
public static void onMethodEnter(@AnnotationValueExtractor(annotationClassName = "co.elastic.apm.api.CaptureSpan", method = "value") String spanName) {
    if (spanName.equals("foo")) {
        // do something special
    }
}

public class NeedsLazyToOneNoProxy<T extends AnnotationSource> extends ElementMatcher.Junction.AbstractBase<T> {


    public boolean matches(T target) {
        AnnotationDescription oneToOneAnnotation = target.getDeclaredAnnotations().ofType(OneToOne.class);
        try {
            if (oneToOneAnnotation != null) {
                OneToOne oneToOne = (OneToOne) ((AnnotationDescription.Loadable) oneToOneAnnotation).load();
                FetchType fetchType = oneToOne.fetch();
                return fetchType == FetchType.LAZY;
            }
            return false;
        }
        catch (ClassNotFoundException e) {
            throw new RuntimeException(e.getMessage(), e);
        }

    }
}

newbytebuddy（）
.重新定义（）
.场(
ElementMatchers.isAnnotatedWith（）
)
...

我想做的是进一步细化我的ElementMatcher，以便在指定的注释中包含一个属性检查-类似这样：

new ByteBuddy()
        .redefine(<some class>)
        .field(
            ElementMatchers.isAnnotatedWith(<some annotation>)
        )
        ...

new ByteBuddy()
        .redefine(<some class>)
        .field(
            ElementMatchers.isAnnotatedWith(<some annotation>)
                .havingAttribute(<some attribute>, "value")
        )

@Advice.OnMethodEnter(suppress = Throwable.class)
public static void onMethodEnter(@AnnotationValueExtractor(annotationClassName = "co.elastic.apm.api.CaptureSpan", method = "value") String spanName) {
    if (spanName.equals("foo")) {
        // do something special
    }
}

public class NeedsLazyToOneNoProxy<T extends AnnotationSource> extends ElementMatcher.Junction.AbstractBase<T> {


    public boolean matches(T target) {
        AnnotationDescription oneToOneAnnotation = target.getDeclaredAnnotations().ofType(OneToOne.class);
        try {
            if (oneToOneAnnotation != null) {
                OneToOne oneToOne = (OneToOne) ((AnnotationDescription.Loadable) oneToOneAnnotation).load();
                FetchType fetchType = oneToOne.fetch();
                return fetchType == FetchType.LAZY;
            }
            return false;
        }
        catch (ClassNotFoundException e) {
            throw new RuntimeException(e.getMessage(), e);
        }

    }
}

newbytebuddy（）
.重新定义（）
.场(
ElementMatchers.isAnnotatedWith（）
.具有属性（，“值”）
)

---

我要找的是做“有属性”部分的方法。这是可能的还是我走错了路？任何见解都值得赞赏。

一种方法是创建一个

Advice.OffsetMapping.Factory

，它允许您在建议中注入注释值，如下所示：

new ByteBuddy()
        .redefine(<some class>)
        .field(
            ElementMatchers.isAnnotatedWith(<some annotation>)
        )
        ...

new ByteBuddy()
        .redefine(<some class>)
        .field(
            ElementMatchers.isAnnotatedWith(<some annotation>)
                .havingAttribute(<some attribute>, "value")
        )

@Advice.OnMethodEnter(suppress = Throwable.class)
public static void onMethodEnter(@AnnotationValueExtractor(annotationClassName = "co.elastic.apm.api.CaptureSpan", method = "value") String spanName) {
    if (spanName.equals("foo")) {
        // do something special
    }
}

public class NeedsLazyToOneNoProxy<T extends AnnotationSource> extends ElementMatcher.Junction.AbstractBase<T> {


    public boolean matches(T target) {
        AnnotationDescription oneToOneAnnotation = target.getDeclaredAnnotations().ofType(OneToOne.class);
        try {
            if (oneToOneAnnotation != null) {
                OneToOne oneToOne = (OneToOne) ((AnnotationDescription.Loadable) oneToOneAnnotation).load();
                FetchType fetchType = oneToOne.fetch();
                return fetchType == FetchType.LAZY;
            }
            return false;
        }
        catch (ClassNotFoundException e) {
            throw new RuntimeException(e.getMessage(), e);
        }

    }
}

另见：

---

我最终实现了一个自定义ElementMatcher，如下所示：

new ByteBuddy()
        .redefine(<some class>)
        .field(
            ElementMatchers.isAnnotatedWith(<some annotation>)
        )
        ...

new ByteBuddy()
        .redefine(<some class>)
        .field(
            ElementMatchers.isAnnotatedWith(<some annotation>)
                .havingAttribute(<some attribute>, "value")
        )

@Advice.OnMethodEnter(suppress = Throwable.class)
public static void onMethodEnter(@AnnotationValueExtractor(annotationClassName = "co.elastic.apm.api.CaptureSpan", method = "value") String spanName) {
    if (spanName.equals("foo")) {
        // do something special
    }
}

public class NeedsLazyToOneNoProxy<T extends AnnotationSource> extends ElementMatcher.Junction.AbstractBase<T> {


    public boolean matches(T target) {
        AnnotationDescription oneToOneAnnotation = target.getDeclaredAnnotations().ofType(OneToOne.class);
        try {
            if (oneToOneAnnotation != null) {
                OneToOne oneToOne = (OneToOne) ((AnnotationDescription.Loadable) oneToOneAnnotation).load();
                FetchType fetchType = oneToOne.fetch();
                return fetchType == FetchType.LAZY;
            }
            return false;
        }
        catch (ClassNotFoundException e) {
            throw new RuntimeException(e.getMessage(), e);
        }

    }
}

公共类NeedsAzytoonenoproxy扩展了ElementMatcher.Junction.AbstractBase{
公共布尔匹配（T目标）{
AnnotationDescription oneToOneAnnotation=target.getDeclaredAnnotations（），类型为（OneToOne.class）；
试一试{
if（onetooneanotation！=null）{
OneToOne OneToOne=（OneToOne）（（AnnotationDescription.Loadable）onetooneanotation.load（）；
FetchType FetchType=oneToOne.fetch（）；
返回fetchType==fetchType.LAZY；
}
返回false；
}
catch（classnotfounde异常）{
抛出新的RuntimeException（e.getMessage（），e）；
}
}
}

---

我使用此元素匹配器来确定是否应该向现有的@OneToOne关系添加@LazyToOne注释。

我是ByteBuddy的初学者，在@Advice注释方面没有跟上速度。我不知道我怎样才能用它来解决我的特殊问题。相反，我最终要做的是实现一个自定义ElementMatcher，它查找我感兴趣的特定注释，加载此注释，然后检查加载的注释上的属性值。不确定这是否是推荐的方法，但它起了作用。加载注释通常很好。我会避免在您的解决方案中使用强制转换，您可以使用Byte Buddy的API实现这一点。如果基础注释已经来自加载的类型，则基本上只需使用hoods下的反射API来访问它。