Jackson JsonMappingException：无法反序列化实例

时间：2014-07-12 04:25:54

标签： java android json jackson

我正在尝试使用Jackson将我的json数据转换为POJO对象。这是MainActivity和我的POJO类代码。我基本上得到一个JsonMappingException错误。我还附上了整个日志。

MainActivity.java：

ObjectMapper mapper = new ObjectMapper();
    mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
    try {
        List<Entries> results = mapper.readValue(new URL("http://collegewires.com/android/jacksoncw.json"), new TypeReference<List<Entries>>(){});
        for(int i=0;i<results.size();++i){
            System.out.println(results.get(i).getName());
            out = out + " ## " + results.get(i).getName();
            txt.setText("1111");
        }
    } catch (JsonParseException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();

    } catch (JsonMappingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();

    } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

Entries.java（这是POJO）

package com.collegewires.jackson;

public class Entries {
public Entries(){
}

private String id, name, email, address, gender;
private Phone phone;

public Phone getPhone() {
    return phone;
}

public void setPhone(Phone phone) {
    this.phone = phone;
}

public String getId() {
    return id;
}

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

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getEmail() {
    return email;
}

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

public String getAddress() {
    return address;
}

public void setAddress(String address) {
    this.address = address;
}

public String getGender() {
    return gender;
}

public void setGender(String gender) {
    this.gender = gender;
}

@Override
public String toString() {
    return "Entries:{id: " + id + ", name: " + name + 
                ", email: " + email + ", address: " + address + ", gender: " + gender + ", phone: " + phone + "}";
}

public class Phone {
    public Phone(){
    }
    public String  mobile, home, office;
    public String getMobile() {
        return mobile;
    }

    public void setMobile(String mobile) {
        this.mobile = mobile;
    }

    public String getHome() {
        return home;
    }

    public void setHome(String home) {
        this.home = home;
    }

    public String getOffice() {
        return office;
    }

    public void setOffice(String office) {
        this.office = office;
    }

    @Override
    public String toString() {
        return "Phone:{mobile: " + mobile + ", home: " + home + 
                    ", office: " + office + "}";
    }
}


}

现在，我的日志中出现以下错误。因此，我无法继续工作。这是日志：

07-12 12:06:13.206: W/System.err(30593): 

com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token
07-12 12:06:13.206: W/System.err(30593):  at [Source: http://collegewires.com/android/jacksoncw.json; line: 1, column: 1]
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:575)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:569)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.handleNonArray(CollectionDeserializer.java:259)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:217)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:207)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:23)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
07-12 12:06:13.211: W/System.err(30593):    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2018)
07-12 12:06:13.211: W/System.err(30593):    at com.collegewires.jackson.MainActivity.onCreate(MainActivity.java:81)
07-12 12:06:13.211: W/System.err(30593):    at android.app.Activity.performCreate(Activity.java:5250)
07-12 12:06:13.211: W/System.err(30593):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1097)
07-12 12:06:13.211: W/System.err(30593):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
07-12 12:06:13.211: W/System.err(30593):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2297)
07-12 12:06:13.211: W/System.err(30593):    at android.app.ActivityThread.access$700(ActivityThread.java:152)
07-12 12:06:13.211: W/System.err(30593):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1282)
07-12 12:06:13.211: W/System.err(30593):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-12 12:06:13.211: W/System.err(30593):    at android.os.Looper.loop(Looper.java:137)
07-12 12:06:13.211: W/System.err(30593):    at android.app.ActivityThread.main(ActivityThread.java:5328)
07-12 12:06:13.211: W/System.err(30593):    at java.lang.reflect.Method.invokeNative(Native Method)
07-12 12:06:13.211: W/System.err(30593):    at java.lang.reflect.Method.invoke(Method.java:511)
07-12 12:06:13.211: W/System.err(30593):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
07-12 12:06:13.211: W/System.err(30593):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
07-12 12:06:13.211: W/System.err(30593):    at dalvik.system.NativeStart.main(Native Method)
07-12 12:06:13.251: D/libEGL(30593): loaded /vendor/lib/egl/libEGL_POWERVR_SGX544_115.so
07-12 12:06:13.261: D/libEGL(30593): loaded /vendor/lib/egl/libGLESv1_CM_POWERVR_SGX544_115.so
07-12 12:06:13.266: D/libEGL(30593): loaded /vendor/lib/egl/libGLESv2_POWERVR_SGX544_115.so
07-12 12:06:13.271: I/(30593): !@IMGSRV: DATE: 2013.04.23(11:19:33) | BUILDER: LSI3D | REVISION: e9cd1377d8225457ae40
07-12 12:06:13.346: D/OpenGLRenderer(30593): Enabling debug mode 0
07-12 12:06:31.521: W/IInputConnectionWrapper(30593): setComposingText on inactive InputConnection

4 个答案:

答案 0 :(得分：10)

Can not deserialize instance of java.util.ArrayList out of START_OBJECT token

这里的关键词是 ArrayList 和 START_OBJECT令牌。您不能将单个对象反序列化为对象数组。尝试理解这样做，你会明白为什么。

您只能将JSON对象的数组反序列化为POJO的数组或集合。请注意，虽然JSON对象由{ }括号分隔，但数组由[ ]括号分隔，其中包含一定数量的对象。

答案 1 :(得分：1)

  1. 删除条目＆amp;中的构造函数的电话

  2. GetEntries results = mapper.readValue(new URL("http://collegewires.com/android/jacksoncw.json"), GetEntries.class);

  3. 条目似乎是JSON中的参数。

    4. <强> GetEntries.java 

    package com.collegewires.jackson;

import java.util.List;

public class GetEntries{
    private List<Entries> entries;

    public List<Entries> getEntries(){
        return this.entries;
    }
    public void setEntries(List<Entries> entries){
        this.entries = entries;
    }
}

    <强> Entries.java 

    package com.collegewires.jackson;

import java.util.List;

public class Entries{
    private String address;
    private String email;
    private String gender;
    private String id;
    private String name;
    private Phone phone;

    public String getAddress(){
        return this.address;
    }
    public void setAddress(String address){
        this.address = address;
    }
    public String getEmail(){
        return this.email;
    }
    public void setEmail(String email){
        this.email = email;
    }
    public String getGender(){
        return this.gender;
    }
    public void setGender(String gender){
        this.gender = gender;
    }
    public String getId(){
        return this.id;
    }
    public void setId(String id){
        this.id = id;
    }
    public String getName(){
        return this.name;
    }
    public void setName(String name){
        this.name = name;
    }
    public Phone getPhone(){
        return this.phone;
    }
    public void setPhone(Phone phone){
        this.phone = phone;
    }
}

    <强> Phone.java 

    package com.collegewires.jackson;

import java.util.List;

public class Phone{
    private String home;
    private String mobile;
    private String office;

    public String getHome(){
        return this.home;
    }
    public void setHome(String home){
        this.home = home;
    }
    public String getMobile(){
        return this.mobile;
    }
    public void setMobile(String mobile){
        this.mobile = mobile;
    }
    public String getOffice(){
        return this.office;
    }
    public void setOffice(String office){
        this.office = office;
    }
}

答案 2 :(得分：0)

json的结构意味着你在这样的对象中读回它：

class Response{
 private List<Entries> entries = ....
public setEntries(List<Entrie> e)
public getEntries()....

}

并像这样加载

 Response results = mapper.readValue(new URL("http://collegewires.com/android/jacksoncw.json"), Response.class);

答案 3 :(得分：0)

只需将数据放入[]而不是{}即可。

例如：

[
    {
        "id": "1",
        "name":"exemple"
    }
]
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