Question

环境详情

我有三个项目：

项目A ：Java REST服务应用程序
项目B ：Java客户端应用
项目C ：一个简单的POJO列表

前两个项目的第三个是依赖项。

数据流

项目B 向项目A 发出 HTTP 请求，该请求使用 Project C 转换的模型对象进行回复它是 JSON 。

项目B 使用JSONObject对 JSON 响应进行解码，并尝试使用BeanUtils获取原始POJO对象。

代码示例

ExamplePOJO类（ Project C 的一部分）：

public class ExamplePOJO {

    private String id;

    private AnotherPOJO anotherPOJO;

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

    public String getId() {
         return id;
    }

    public void setAnotherPOJO(AnotherPOJO anotherPOJO ) {
         this.anotherPOJO = anotherPOJO ;
    }

    public AnotherPOJO getAnotherPOJO() {
         return anotherPOJO ;
    }

}

项目A 示例端点：

@Path("/sample")
@GET
@Produces(MediaType.APPLICATION_JSON)
public Response getExampleResponse() {

    try {

        ServiceResponse<ExamplePOJO> response = new ServiceResponse<ExamplePOJO>();

        ExamplePOJO eo = new ExamplePOJO();
        eo.setId("1");

        AnotherPOJO ap = new AnotherPOJO();
        eo.setAnotherPojo(ap);

        response.setResponse(eo);

        return ((ResponseBuilder) Response.ok().entity(response)).type("application/json").build();

    } catch(Exception E) {
        //error
    }
}

项目A 响应对象容器：

public class ServiceResponse<T> {

    private T response;

    public T getResponse() {
        return this.response;
    }

    public void setResponse(T response) {
         this.response = response;
    }

}

有趣的部分，项目B ：

public void callService() {

    //....HTTP request...

    //json object
    JSONObject json = new JSONObject(jsonResponse);

    //ServiceResponseEquivalent is the same as the ServiceResponse object of *Project A*
    decodeResponse(json, ServiceResponseEquivalent.class, ExamplePOJO.class);

}


//this is a recursive function
public <T, V> T void decodeResponse(JSONObject json, Class<?> responseModel, Class<V> responseObjectModel) {

    //this is the same as the ServiceResponse object of *Project A*
    Object reflectedInstance = responseModel.newInstance();

    //here I got the field "response" of ServiceResponse
    Field[] fields = reflectedInstance.getClass().getDeclaredFields();
    for(Field field: fields) {

         //I got the json object based on the field name
         Object objectFromResponse = json.get(field.getName());

         if(objectFromResponse instanceof JSONObject) {

             //this is the "response" property of *ServiceResponse* which I know is an instance of *ExamplePOJO* class (because who calls this function pass *Class<V> responseObjectModel*
             if(if(field.getName().equals("response")) {

                  //recursive call
                  objectFromResponse = decodeResponse(json.getJSONObject(field.getName()), responseObjectModel, responseObjectModel);
             } 
             //here I found another object inside the "response" object but I don't know which class is it. In this case it's an instance of *AnotherPOJO*
             else {

                 //I try to get the class from the name of the property: in order to work, the property must be named as its class
                 String className = "com.example.packace." + field.getName().toUpperCase().charAt(0) + field.getName().substring(1, field.getName().length());

                //className = com.example.package.AnotherPOJO                       
                //recursive call
                objectFromResponse = decodeResponse(json.getJSONObject(field.getName()), Class.forName(className), responseObjectModel);

                //I try to set the object inside the response one
                //HERE IT FAILS
                BeanUtils.setProperty(reflectedInstance, field.getName(), objectFromResponse);

             }
             //here we found another Object but we don't know 
         } else {

             //I add the element
             BeanUtils.setProperty(reflectedInstance, field.getName(), objectFromResponse);
         }
    }

}

JSON示例

客户端收到此 JSON ：

{
    "response": { //response is an instance of ExamplePOJO
        "id":"1",
        "anotherPOJO":{
             [...]
        }
    },
    [ ...other fields...]
 }

问题

当 decodeResponse 尝试解码递归调用中的 AnotherPOJO 对象时，会抛出此异常：

java.lang.IllegalArgumentException：无法在bean类'com.example.package.ExamplePOJO'上调用com.example.package.ExamplePOJO.setAnotherPOJO - 参数类型不匹配 - 具有类型为“com.example.package.AnotherPOJO”的对象“但预期签名”com.example.package.AnotherPOJO“

从异常中可以明显看出，对象是同一个类的实例。

有什么想法吗？

这可能是解码未知类对象的更好方法？这样：

String className = "com.example.packace." + field.getName().toUpperCase().charAt(0) + field.getName().substring(1, field.getName().length());

 //className = com.example.package.AnotherPOJO                      
 //recursive call
 objectFromResponse = decodeResponse(json.getJSONObject(field.getName()), Class.forName(className), responseObjectModel);

有明显的问题，必须将该字段命名为其类。

Answer 1

这似乎是类加载问题。查看Class.forName(String)的来源，它使用来自调用者的类加载器。这可能与加载目标responseModel的类加载器不同，因此，请尝试以下操作：

//recursive call
objectFromResponse = decodeResponse(
    json.getJSONObject(field.getName()),
    Class.forName(className, true, responseModel.getClassLoader()),
    responseObjectModel);

这应该确保模型子层次结构类由相同的类加载器加载。

Answer 2

您可以在field变量中获得有关该课程的信息。调用field.getType()获取当前字段/属性的类...

         //here I found another object inside the "response" object.  Use information from field to get class.
         else {

             objectFromResponse = decodeResponse(json.getJSONObject(field.getName()), field.getType(), responseObjectModel);

注意：我建议Jackson将JSON转换为java对象。

BeanUtils setProperty抛出IllegalArgumentException

2 个答案: