java - 无法使用 Java 8 修改 package-info.java 的注解

Question

我遇到了一个问题，我必须修改一个包信息。

包信息.java

@javax.xml.bind.annotation.XmlSchema(namespace = "http://some.url/soap/style/document_literal")
package org.example.wsdl.wsdl;

以下代码适用于 1.7.0_45。

//          do not load any classes before, this could break the following code.
            Class<?> pkgInfo = Class.forName("org.example.wsdl.package-info", true, NameSpaceModifier.class.getClassLoader());
            Field field = Class.class.getDeclaredField("annotations");
            field.setAccessible(true);

            final XmlSchema oldAnnotation = (XmlSchema) pkgInfo.getAnnotations()[0];
            logger.debug("Old Annotation namespace value was: " + oldAnnotation.namespace());
            XmlSchema newAnnotation = new XmlSchema() {

                @Override
                public XmlNs[] xmlns() {
                    return oldAnnotation.xmlns();
                }

                @Override
                public String namespace() {
                    return "newNs";
                }

                @Override
                public XmlNsForm elementFormDefault() {
                    return oldAnnotation.elementFormDefault();
                }

                @Override
                public XmlNsForm attributeFormDefault() {
                    return oldAnnotation.attributeFormDefault();
                }

                @Override
                public String location() {
                    return oldAnnotation.location();
                }

                @Override
                public Class<? extends Annotation> annotationType() {
                    return oldAnnotation.annotationType();
                }
            };

            @SuppressWarnings("unchecked")
            Map<Class<? extends Annotation>, Annotation> annotations = (Map<Class<? extends Annotation>, Annotation>) field.get(pkgInfo);
            annotations.put(XmlSchema.class, newAnnotation);

            XmlSchema modifiedAnnotation = (XmlSchema) pkgInfo.getAnnotations()[0];

当使用 1.8.0_05 编译和执行相同代码时，我收到此错误消息:

java.lang.NoSuchFieldException: annotations
    at java.lang.Class.getDeclaredField(Class.java:2057)

我知道这是一个 Hack，至少它看起来像一个。但是 Java 8 是否按预期在这里工作？ 那么我必须如何更改适用于 Java 8 的代码？

也欢迎 Javasist 回答 ;)

Answer 1

Java 8 改变了注释在内部的存储方式。由于您正在使用带有硬编码字段名称的讨厌的反射 hack，因此任何 Java 更新都有可能重新破坏您的代码。

java.lang.Class:

/**
 * @since 1.5
 */
public Annotation[] getAnnotations() {
    return AnnotationParser.toArray(annotationData().annotations);
}

private volatile transient AnnotationData annotationData;

private AnnotationData annotationData() {
    while (true) { // retry loop
        AnnotationData annotationData = this.annotationData;
        int classRedefinedCount = this.classRedefinedCount;
        if (annotationData != null &&
            annotationData.redefinedCount == classRedefinedCount) {
            return annotationData;
        }
        // null or stale annotationData -> optimistically create new instance
        AnnotationData newAnnotationData = createAnnotationData(classRedefinedCount);
        // try to install it
        if (Atomic.casAnnotationData(this, annotationData, newAnnotationData)) {
            // successfully installed new AnnotationData
            return newAnnotationData;
        }
    }
}

private static class AnnotationData {
    final Map<Class<? extends Annotation>, Annotation> annotations;
    final Map<Class<? extends Annotation>, Annotation> declaredAnnotations;

    // Value of classRedefinedCount when we created this AnnotationData instance
    final int redefinedCount;

    AnnotationData(Map<Class<? extends Annotation>, Annotation> annotations,
                   Map<Class<? extends Annotation>, Annotation> declaredAnnotations,
                   int redefinedCount) {
        this.annotations = annotations;
        this.declaredAnnotations = declaredAnnotations;
        this.redefinedCount = redefinedCount;
    }
}

我想您可以使用新的字段值来临时修复您的代码。永久修复是更改注释本身，而不是在运行时动态修改它。

Field annotationDataField = Class.class.getDeclaredField("annotationData");
annotationDataField.setAccessible(true);

Object annotationData = annotationDataField.get(pkgInfo);

Field annotationsField = annotationData.getClass().getDeclaredField("annotations");
annotationsField.setAccessible(true);

Map<Class<? extends Annotation>, Annotation> annotations = (Map<Class<? extends Annotation>, Annotation>) annotationsField
        .get(annotationData);
annotations.put(XmlSchema.class, newAnnotation);

XmlSchema modifiedAnnotation = (XmlSchema) pkgInfo.getAnnotations()[0];