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jackson jsondersializer堆栈溢出

jackson java

Frank Kong · 技术社区 · 6 年前

我试图从Java中的json标记中提取属性,并编写jsondeserizer来完成这项工作。
我的尝试如下:

public class testJacksonSimple {
    @JsonDeserialize(using = ItemDeserializerJson.class)
    public static class Item {
        public int id;
        public String itemName;

        public Item(){};
        public Item(int id, String itemName) {
            this.id = id;
            this.itemName = itemName;
        }

        public void setId(int id) {
            this.id = id;
        }

        public int getId() {
            return id;
        }
    }

    public static class ItemDeserializerJson extends JsonDeserializer<Item> {

        ObjectReader reader = new ObjectMapper().reader();

        @Override
        public Item deserialize(JsonParser jp, DeserializationContext context) throws IOException {
            if(jp.currentToken() != JsonToken.VALUE_NULL) {
                return reader.readValue(jp, Item.class);
            } else {
                return null;
            }
        }
    }
}

这是我的测试用例:

public class test {
    public static void main(String[] args){
        ObjectMapper mapper = new ObjectMapper();
        String json = "{\n" +
                "    \"id\": 1,\n" +
                "    \"itemName\": \"theItem\"\n" +
                "}";
        System.out.println(json);
        testJacksonSimple.Item itemWithOwner = null;
        try {
            itemWithOwner = new ObjectMapper().readValue(json, testJacksonSimple.Item.class);
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println(itemWithOwner.id);
        System.out.println(itemWithOwner.itemName);
    }
}

我搞错了:

Exception in thread "main" java.lang.StackOverflowError
    at java.lang.reflect.Method.getParameterTypes(Method.java:264)
    at sun.reflect.annotation.AnnotationInvocationHandler.invoke(AnnotationInvocationHandler.java:59)
    at com.sun.proxy.$Proxy2.annotationType(Unknown Source)
    at com.fasterxml.jackson.databind.introspect.AnnotationMap._add(AnnotationMap.java:135)
    at com.fasterxml.jackson.databind.introspect.AnnotationMap.addIfNotPresent(AnnotationMap.java:101)
    at com.fasterxml.jackson.databind.introspect.AnnotatedClass._addAnnotationsIfNotPresent(AnnotatedClass.java:1061)
    at com.fasterxml.jackson.databind.introspect.AnnotatedClass._resolveClassAnnotations(AnnotatedClass.java:399)
    at com.fasterxml.jackson.databind.introspect.AnnotatedClass._classAnnotations(AnnotatedClass.java:376)
    at com.fasterxml.jackson.databind.introspect.AnnotatedClass.getAnnotation(AnnotatedClass.java:248)
    at com.fasterxml.jackson.databind.AnnotationIntrospector._findAnnotation(AnnotationIntrospector.java:1436)
    at com.fasterxml.jackson.databind.introspect.JacksonAnnotationIntrospector.findAutoDetectVisibility(JacksonAnnotationIntrospector.java:349)
    at com.fasterxml.jackson.databind.introspect.POJOPropertiesCollector.<init>(POJOPropertiesCollector.java:129)

只是不明白为什么我得到错误堆栈溢出。我可以不使用自定义jsondersializer获得正确的结果,但我想测试它。如有任何帮助,我们将不胜感激。

2 回复 | 直到 6 年前

Justin.Cooke 6 年前

通过调用objectmapper并请求它从自定义反序列化程序内部反序列化json,您创建了一个无限循环。对象映射器正在调用自定义反序列化程序,然后自定义反序列化程序正在调用对象映射器。因此堆栈溢出。

以下对我有效:

    public static class ItemDeserializerJson extends JsonDeserializer<Item> {

    @Override
    public Item deserialize(JsonParser jp, DeserializationContext context) throws IOException {

        JsonNode node = jp.getCodec().readTree(jp);
        int id = (Integer) (node.get("id")).numberValue();
        String itemName = node.get("itemName").asText();

        return new Item(id, itemName);
    }
}

standy 6 年前

所以基本上 reader.readValue(jp, Item.class); 将重复调用反序列化方法。顺便说一下,请遵守命名约定(类名应该是大写的camelcase): http://www.oracle.com/technetwork/java/javase/overview/codeconventions-135099.html