java - 将 Java 对象保存到 JSON 时出现 JsonMappingException

Question

 org.codehaus.jackson.map.JsonMappingException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) ) through reference chain..

上面是我遇到的异常，我的 pojo 中的非原始成员变量无法读取。经过几次搜索后，我尝试为 POJO 类添加 @JsonAutoDetect ，并尝试为所有未识别的字段添加 @JsonProperty 注释。这不起作用，所以我也尝试了 @JsonIgnoreProperties({"hibernateLazyInitializer", "handler"}) 但也没有运气。

这是我尝试将对象转换为 json 的地方:

@Override
public Map<String, String> getChanges(User oldInfo, User newInfo) {
    oldAndNewInfo = new HashMap<String, String>();
    objectWriter = new ObjectMapper().writer().withDefaultPrettyPrinter();
    try {
        oldAndNewInfo.put(objectWriter.writeValueAsString(oldInfo), objectWriter.writeValueAsString(newInfo));
    } catch (Exception e) {
        e.printStackTrace(ps);
    }
    return oldAndNewInfo;
}

有人有什么想法吗？

Answer 1

我认为您应该禁用 SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS 属性。

保持对象映射器内联的一个好方法(并且作为最佳实践)最好将它们保存在某种模块中。

protected 单例，Guice 配置，Spring 配置，一些单例的存储位置。我将在我的示例中使用 protected 单例，但这几乎就是文档所说的。

还请记住，用于 xml 或 json 的对象映射器的构建成本非常昂贵。如果您进行了大量序列化，请保存它

public abstract class JsonConfig{

    private JsonConfig(){

    }

    private static final ObjectMapper CONFIGURED_OBJECT_MAPPER;
    private static final JacksonJsonProvider JAX_RS_JSON_PROVIDER;

    static{
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        objectMapper.configure(SerializationFeature.WRAP_ROOT_VALUE, false);
        objectMapper.configure(DeserializationFeature.USE_BIG_DECIMAL_FOR_FLOATS, true);
        objectMapper.configure(SerializationFeature.WRITE_EMPTY_JSON_ARRAYS, true);

        //and just incase you do some web transformaions with jersy or something

        JAX_RS_JSON_PROVIDER = new JacksonJsonProvider(objectMapper);

        CONFIGURED_OBJECT_MAPPER = objectMapper;    
    }

    public static ObjectMapper getObjectMapperInstance(){
        return CONFIGURED_OBJECT_MAPPER;
    }

    public static JacksonJsonProvider getJsonProviderInstance(){
       return return JAX_RS_JSON_PROVIDER
    }
}