JSON解析与Robospice

Question

我正在使用Robospice构建一个Android应用程序，通过网络进行通信。从我的服务器返回的结果对象不能正确地反序列化。以下是相关的课程：

UserRequest.java

import com.google.api.client.http.GenericUrl;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.json.jackson.JacksonFactory;
import com.octo.android.robospice.request.googlehttpclient.GoogleHttpClientSpiceRequest;

import roboguice.util.temp.Ln;
import trees.park.cal.smoke.models.UserList;

public class UserRequest extends GoogleHttpClientSpiceRequest<UserList>{

    private String baseUrl = "http://10.0.0.3:8181/users/";

    public UserRequest() {
        super(UserList.class);
    }

    @Override
    public UserList loadDataFromNetwork() throws Exception {
        Ln.d("Call web service " + baseUrl);
        HttpRequest request = getHttpRequestFactory()
                .buildGetRequest(new GenericUrl(baseUrl));
        request.setParser( new JacksonFactory().createJsonObjectParser() );
        HttpResponse response = request.execute();
        return response.parseAs( getResultType() );
    }
}

UserList.java

import java.util.ArrayList;

public class UserList extends ArrayList<User> {
}

User.java

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;

import java.util.Collections;
import java.util.List;

public class User {

    @JsonProperty("id")private long id;
    @JsonProperty("email")private String email;
    @JsonProperty("password")private String password;

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public long getId() {
        return id;
    }

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

    @JsonCreator
    public User(@JsonProperty("id") long id, @JsonProperty("email") String email, @JsonProperty("password") String password) {
        this.id = id;
        this.email = email;
        this.password = password;
    }

}

调用response.parseAs(getRequestType())时，将使用以下堆栈跟踪引发异常：

08-19 23:54:08.411  27117-27139/trees.park.cal.smoke E//DefaultRequestRunner.java:154﹕ 23:54:08.418 Thread-5533 An exception occurred during request network execution :
    java.lang.IllegalArgumentException:
            at com.google.api.client.json.JsonParser.parseValue(JsonParser.java:880)
            at com.google.api.client.json.JsonParser.parse(JsonParser.java:381)
            at com.google.api.client.json.JsonParser.parse(JsonParser.java:354)
            at com.google.api.client.json.JsonObjectParser.parseAndClose(JsonObjectParser.java:87)
            at com.google.api.client.json.JsonObjectParser.parseAndClose(JsonObjectParser.java:81)
            at com.google.api.client.http.HttpResponse.parseAs(HttpResponse.java:459)
            at trees.park.cal.smoke.server.UserRequest.loadDataFromNetwork(UserRequest.java:27)
            at trees.park.cal.smoke.server.UserRequest.loadDataFromNetwork(UserRequest.java:12)
            at com.octo.android.robospice.request.CachedSpiceRequest.loadDataFromNetwork(CachedSpiceRequest.java:48)
            at com.octo.android.robospice.request.DefaultRequestRunner.processRequest(DefaultRequestRunner.java:150)
            at com.octo.android.robospice.request.DefaultRequestRunner$1.run(DefaultRequestRunner.java:217)
            at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:422)
            at java.util.concurrent.FutureTask.run(FutureTask.java:237)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
            at java.lang.Thread.run(Thread.java:841)
     Caused by: java.lang.IllegalArgumentException:
            at com.google.api.client.json.JsonParser.parseValue(JsonParser.java:880)
            at com.google.api.client.json.JsonParser.parseArray(JsonParser.java:647)
            at com.google.api.client.json.JsonParser.parseValue(JsonParser.java:739)
            at com.google.api.client.json.JsonParser.parse(JsonParser.java:381)
            at com.google.api.client.json.JsonParser.parse(JsonParser.java:354)
            at com.google.api.client.json.JsonObjectParser.parseAndClose(JsonObjectParser.java:87)
            at com.google.api.client.json.JsonObjectParser.parseAndClose(JsonObjectParser.java:81)
            at com.google.api.client.http.HttpResponse.parseAs(HttpResponse.java:459)
            at trees.park.cal.smoke.server.UserRequest.loadDataFromNetwork(UserRequest.java:27)
            at trees.park.cal.smoke.server.UserRequest.loadDataFromNetwork(UserRequest.java:12)
            at com.octo.android.robospice.request.CachedSpiceRequest.loadDataFromNetwork(CachedSpiceRequest.java:48)
            at com.octo.android.robospice.request.DefaultRequestRunner.processRequest(DefaultRequestRunner.java:150)
            at com.octo.android.robospice.request.DefaultRequestRunner$1.run(DefaultRequestRunner.java:217)
            at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:422)
            at java.util.concurrent.FutureTask.run(FutureTask.java:237)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
            at java.lang.Thread.run(Thread.java:841)
     Caused by: java.lang.IllegalArgumentException: unable to create new instance of class trees.park.cal.smoke.models.User because it has no accessible default constructor
            at com.google.api.client.util.Types.handleExceptionForNewInstance(Types.java:165)
            at com.google.api.client.util.Types.newInstance(Types.java:120)
            at com.google.api.client.json.JsonParser.parseValue(JsonParser.java:763)
            at com.google.api.client.json.JsonParser.parseArray(JsonParser.java:647)
            at com.google.api.client.json.JsonParser.parseValue(JsonParser.java:739)
            at com.google.api.client.json.JsonParser.parse(JsonParser.java:381)
            at com.google.api.client.json.JsonParser.parse(JsonParser.java:354)
            at com.google.api.client.json.JsonObjectParser.parseAndClose(JsonObjectParser.java:87)
            at com.google.api.client.json.JsonObjectParser.parseAndClose(JsonObjectParser.java:81)
            at com.google.api.client.http.HttpResponse.parseAs(HttpResponse.java:459)
            at trees.park.cal.smoke.server.UserRequest.loadDataFromNetwork(UserRequest.java:27)
            at trees.park.cal.smoke.server.UserRequest.loadDataFromNetwork(UserRequest.java:12)
            at com.octo.android.robospice.request.CachedSpiceRequest.loadDataFromNetwork(CachedSpiceRequest.java:48)
            at com.octo.android.robospice.request.DefaultRequestRunner.processRequest(DefaultRequestRunner.java:150)
            at com.octo.android.robospice.request.DefaultRequestRunner$1.run(DefaultRequestRunner.java:217)
            at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:422)
            at java.util.concurrent.FutureTask.run(FutureTask.java:237)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
            at java.lang.Thread.run(Thread.java:841)
     Caused by: java.lang.InstantiationException: can't instantiate class trees.park.cal.smoke.models.User; no empty constructor
            at java.lang.Class.newInstanceImpl(Native Method)
            at java.lang.Class.newInstance(Class.java:1208)
            at com.google.api.client.util.Types.newInstance(Types.java:116)
            at com.google.api.client.json.JsonParser.parseValue(JsonParser.java:763)
            at com.google.api.client.json.JsonParser.parseArray(JsonParser.java:647)
            at com.google.api.client.json.JsonParser.parseValue(JsonParser.java:739)
            at com.google.api.client.json.JsonParser.parse(JsonParser.java:381)
            at com.google.api.client.json.JsonParser.parse(JsonParser.java:354)
            at com.google.api.client.json.JsonObjectParser.parseAndClose(JsonObjectParser.java:87)
            at com.google.api.client.json.JsonObjectParser.parseAndClose(JsonObjectParser.java:81)
            at com.google.api.client.http.HttpResponse.parseAs(HttpResponse.java:459)
            at trees.park.cal.smoke.server.UserRequest.loadDataFromNetwork(UserRequest.java:27)
            at trees.park.cal.smoke.server.UserRequest.loadDataFromNetwork(UserRequest.java:12)
            at com.octo.android.robospice.request.CachedSpiceRequest.loadDataFromNetwork(CachedSpiceRequest.java:48)
            at com.octo.android.robospice.request.DefaultRequestRunner.processRequest(DefaultRequestRunner.java:150)
            at com.octo.android.robospice.request.DefaultRequestRunner$1.run(DefaultRequestRunner.java:217)
            at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:422)
            at java.util.concurrent.FutureTask.run(FutureTask.java:237)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
            at java.lang.Thread.run(Thread.java:841)

但是，如果我使用一个ObjectMapper，反序列化就会完美无缺地发生。在我的LoginActivity (我刚刚为测试目的编写的)中可以找到一个示例：

public class LoginActivity extends Activity{

    private SpiceManager spiceManager = new SpiceManager(JacksonGoogleHttpClientSpiceService.class);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);

        String json = "[\n" +
                "    {\n" +
                "        \"id\": 1, \n" +
                "        \"email\": \"michaeldubyu@gmail.com\", \n" +
                "        \"password\": \"password\"\n" +
                "    }, \n" +
                "    {\n" +
                "        \"id\": 2, \n" +
                "        \"email\": \"asdf@adsf.com\", \n" +
                "        \"password\": \"\"\n" +
                "    }, \n" +
                "    {\n" +
                "        \"id\": 3, \n" +
                "        \"email\": \"paymahn1@gmail.com\", \n" +
                "        \"password\": \"\"\n" +
                "    }, \n" +
                "    {\n" +
                "        \"id\": 4, \n" +
                "        \"email\": \"michaeasdfldubyu@gmail.com\", \n" +
                "        \"password\": \"password\"\n" +
                "    }\n" +
                "]";
        ObjectMapper mapper = new ObjectMapper();
        try {
            UserList result = mapper.readValue(json, UserList.class);
            System.out.println("test");

        } catch (IOException e) {
            e.printStackTrace();
        }

        //stuff
    }
}

如果手动将response.parseAs(getRequestType())替换为ObjectMapper，然后手动从HttpResponse获取输入流，那么我就可以完全反序列化响应。

为什么JsonObjectParser不能像ObjectMapper那样做呢？我怎样才能解决这个问题？

谢谢

Answer 1

答案在堆栈中

由：no empty constructor java.lang.InstantiationException: can't instantiate class trees.park.cal.smoke.models.User;引起

尝试将没有参数的构造器添加到User类

public User() {
}