使用 XStream 1.4.2 反序列化瞬态字段

Question

我遇到了使用 XStream 1.4.2 反序列化可能是瞬态的字段的要求。尽管如此，这些字段可能会同时使用@XStreamAlias 和@XStreamAsAttribute 进行注释。是的，我知道，这听起来很奇怪，这表明设计不好，但这是我目前所拥有的。由于 XStream 提供了一种指定自定义转换器的方法，因此我尝试扩展 com.thoughtworks.xstream.converters.reflection.ReflectionConverter 以覆盖忽略所有瞬态字段的默认方法，以使 XStream 允许反序列化它们。但是，我完全坚持有两个想法来实现这样的转换器，但它们都不起作用。所以这是我尝试过的：

第一种方法不起作用：

public final class TransientSimpleConverter extends ReflectionConverter {

    private final Class<?> type;

    private TransientSimpleConverter(Class<?> type, Mapper mapper, ReflectionProvider reflectionProvider) {
        super(mapper, reflectionProvider);
        this.type = type;
    }

    public static TransientSimpleConverter transientSimpleConverter(Class<?> type, XStream xStream) {
        return new TransientSimpleConverter(type, xStream.getMapper(), xStream.getReflectionProvider());
    }

    @Override
    protected boolean shouldUnmarshalTransientFields() {
        return true;
    }

    @Override
    public boolean canConvert(Class type) {
        return this.type == type;
    }

}

第二种方式也不行：

public final class TransientComplexConverter extends ReflectionConverter {

    private final Class<?> type;

    private TransientComplexConverter(Class<?> type, Mapper mapper, ReflectionProvider provider) {
        super(mapper, provider);
        this.type = type;
    }

    public static TransientComplexConverter transientComplexConverter(Class<?> type, Mapper mapper, Iterable<String> fieldNames) {
        return new TransientComplexConverter(type, mapper, TransientHackReflectionProvider.transientHackReflectionProvider(type, fieldNames));
    }

    @Override
    public boolean canConvert(Class type) {
        return this.type == type;
    }

    private static final class TransientHackReflectionProvider extends PureJavaReflectionProvider {

        private final Class<?> type;
        private final Collection<Field> allowedFields;
        private final Collection<String> allowedAliases;

        private TransientHackReflectionProvider(Class<?> type, Collection<Field> allowedFields, Collection<String> allowedAliases) {
            this.type = type;
            this.allowedFields = allowedFields;
            this.allowedAliases = allowedAliases;
        }

        public static TransientHackReflectionProvider transientHackReflectionProvider(final Class<?> type, Iterable<String> fieldNames) {
            final Collection<Field> allowedFields = from(fieldNames).transform(new Function<String, Field>() {
                @Override
                public Field apply(String name) {
                    return field(type, name);
                }
            }).toList();
            final Collection<String> allowedAliases = transform(allowedFields, new Function<Field, String>() {
                @Override
                public String apply(Field f) {
                    return f.getName();
                }
            });
            return new TransientHackReflectionProvider(type, allowedFields, allowedAliases);
        }

        @Override
        protected boolean fieldModifiersSupported(Field field) {
            return allowedFields.contains(field) ? true : super.fieldModifiersSupported(field);
        }

        @Override
        public boolean fieldDefinedInClass(String fieldName, Class type) {
            return type == this.type && allowedAliases.contains(fieldName) ? true : super.fieldDefinedInClass(fieldName, type);
        }

        private static final Field field(Class<?> type, String name) {
            try {
                final Field field = type.getDeclaredField(name);
                checkArgument(isTransient(field.getModifiers()), name + " is not transient");
                checkArgument(field.getAnnotation(XStreamAsAttribute.class) != null, name + " must be annotated with XStreamAsAttribute");
                checkArgument(field.getAnnotation(XStreamAlias.class) != null, name + " must be annotated with XStreamAlias");
                return field;
            } catch (final SecurityException ex) {
                throw new RuntimeException(ex);
            } catch (final NoSuchFieldException ex) {
                throw new RuntimeException(ex);
            }
        }

    }

}

对于解决方法有什么建议或想法吗？提前致谢。

Answer 1

我知道这篇文章很旧，但也许有人仍然感兴趣。我的解决方案：

XStream xstream = new XStream(new MyPureJavaReflectionProvider());

class MyPureJavaReflectionProvider extends PureJavaReflectionProvider {

    public MyPureJavaReflectionProvider() {
        this(new FieldDictionary(new ImmutableFieldKeySorter()));
    }

    public MyPureJavaReflectionProvider(FieldDictionary fieldDictionary) {
        super(fieldDictionary);
    }

    protected boolean fieldModifiersSupported(Field field) {
        int modifiers = field.getModifiers();
        return !Modifier.isStatic(modifiers);
    }

    public boolean fieldDefinedInClass(String fieldName, Class type) {
        Field field = fieldDictionary.fieldOrNull(type, fieldName, null);
        return field != null && fieldModifiersSupported(field);
    }   

}