Hazelcast IMDG字符串到HazelcastJsonValue问题

Question

未发生将Hazel cast IMDG字符串转换为HazelcastJsonValue的操作。

发布语句-将json存储为HazelCast IMDG中的字符串格式。使用下面的HazelcastJsonValue ..Getting检索异常

请帮助解决此问题。

如果HazelcastJsonValue对象存储在hazelcast IMDG..起作用了。但String to HazelcastJsonValue不起作用。获取以下异常：

Exception in thread "main" com.hazelcast.query.QueryException: java.lang.IllegalArgumentException: There is no suitable accessor for 'age' on class 'java.lang.String'
    at com.hazelcast.query.impl.getters.ReflectionHelper.createGetter(ReflectionHelper.java:171)
    at com.hazelcast.query.impl.getters.Extractors.instantiateGetter(Extractors.java:152)
    at com.hazelcast.query.impl.getters.Extractors.getGetter(Extractors.java:118)
    at com.hazelcast.query.impl.getters.Extractors.extract(Extractors.java:73) 

public static void main(String args[]) {

    HazelcastInstance instance = com.hazelcast.core.Hazelcast.newHazelcastInstance(config());
    String person1 = "{ \"name\": \"John\", \"age\": 35 }";
    String person2 = "{ \"name\": \"Jane\", \"age\": 24 }";
    String person3 = "{ \"name\": \"Trey\", \"age\": 17 }";
    //Storing as String
    IMap<Integer, String> idPersonMap = instance.getMap("jsonValues");
    idPersonMap.put(1, person1);
    idPersonMap.put(2, person2);
    idPersonMap.put(3, person3);

    //Retrieving as HazelcastJsonValue
    IMap<Integer, HazelcastJsonValue> idPersonMapRead =  instance.getMap("jsonValues");
    Collection<HazelcastJsonValue> peopleUnder21 = (Collection<HazelcastJsonValue>) idPersonMapRead.values(Predicates.lessThan("age", 50));
    System.out.println( "-------------------Result--------------------");
    System.out.println( peopleUnder21.stream().collect(Collectors.toList()));

}

 public static Config config(){
        Config config = new Config();
        config.setInstanceName("hazelcast-instance")
                .addMapConfig(
                        new MapConfig().setMetadataPolicy(MetadataPolicy.OFF)
                                .setName("configuration")
                                .setMaxSizeConfig(new MaxSizeConfig(200, MaxSizeConfig.MaxSizePolicy.FREE_HEAP_SIZE))
                                .setEvictionPolicy(EvictionPolicy.LRU)
                                .setTimeToLiveSeconds(-1));

        return config;
    }

Answer 1

您将String实例放入IMap中。不要期望get操作返回HazelcastJsonValue实例。它将再次成为String。

当你调用get方法时，它并不知道你的目标泛型类型。为了方便用户，Hazelcast没有返回原始类型，但它在底层进行了未经检查的转换。

如果您希望在put操作中实现自动值转换，则可以使用MapInterceptor，例如：

IMap<Integer, String> idPersonMap = instance.getMap("jsonValues");
idPersonMap.addInterceptor(new ConvertOnPutMapInterceptor());

    private static class ConvertOnPutMapInterceptor implements MapInterceptor {

        @Override
        public Object interceptGet(Object value) {
            return value;
        }

        @Override
        public void afterGet(Object value) {
        }

        @Override
        public Object interceptPut(Object oldValue, Object newValue) {
            return new HazelcastJsonValue((String) newValue);
        }

        @Override
        public void afterPut(Object value) {
        }

        @Override
        public Object interceptRemove(Object removedValue) {
            return null;
        }

        @Override
        public void afterRemove(Object value) {
        }
    }