java - 使用 Jettison 进行 JSON 解析

Question

我正在尝试使用 Jettison 解析 JSON 对象。这是我正在使用的代码

String s ="{\"appUsage\":[{\"appName\":\"ANDROID\",\"totalUsers\":\"0\"},{\"appName\":\"IOS\",\"totalUsers\":\"4\"}]}";

JSONObject obj = new JSONObject(s);

ArrayList<MiAppUsage> l1 =  (ArrayList<MiAppUsage>) jsonParser(ArrayList.class, obj);

public static Object jsonParser(Class c, JSONObject obj)
            throws JSONException, XMLStreamException, JAXBException {
        JAXBContext jc = JAXBContext.newInstance(c);
        Configuration config = new Configuration();
        MappedNamespaceConvention con = new MappedNamespaceConvention(config);
        XMLStreamReader xmlStreamReader = new MappedXMLStreamReader(obj, con);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        ArrayList<MiAppUsage>customer = (ArrayList<MiAppUsage>) unmarshaller.unmarshal(xmlStreamReader);
        return customer;
    }

我遇到了这个错误

Exception in thread "main" javax.xml.bind.UnmarshalException - with linked exception: [javax.xml.bind.UnmarshalException: unexpected element (uri:"", local:"appUsage"). Expected elements are (none)] at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.handleStreamException(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal(Unknown Source) at com.json.UnmarshalDemo.jsonParser(UnmarshalDemo.java:56) at com.json.UnmarshalDemo.main(UnmarshalDemo.java:33) Caused by: javax.xml.bind.UnmarshalException: unexpected element (uri:"", local:"appUsage"). Expected elements are (none) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext.handleEvent(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Loader.reportError(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Loader.reportError(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Loader.reportUnexpectedChildElement(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext$DefaultRootLoader.childElement(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext._startElement(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext.startElement(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.InterningXmlVisitor.startElement(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.StAXStreamConnector.handleStartElement(Unknown Source) at com.sun.xml.internal.bind.v2.runtime.unmarshaller.StAXStreamConnector.bridge(Unknown Source) ... 4 more Caused by: javax.xml.bind.UnmarshalException: unexpected element (uri:"", local:"appUsage"). Expected elements are (none) ... 14 more

如何解决这个问题

Answer 1

注意:我是 EclipseLink JAXB (MOXy) 的负责人，也是 JAXB 2 (JSR-222) 专家组的成员。

如果您最终正在寻找一种使用 JAXB (JSR-222) 实现与 JSON 交互的方法，那么下面是如何使用 MOXy 完成的。 Jettison 是一个有趣的库，但使用它时会遇到一些问题:

• http://blog.bdoughan.com/2011/04/jaxb-and-json-via-jettison.html

演示

仅使用标准的 Java SE API。有两个 MOXy 特定属性需要在 Unmarshaller 上设置:“eclipselink.media-type” 以指定 “application/json” , 和 "eclipselink.json.include-root" 表示没有根节点。

package forum9924567;

import java.io.StringReader;
import java.util.ArrayList;

import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;

public class Demo {

    private static final String s ="{\"appUsage\":[{\"appName\":\"ANDROID\",\"totalUsers\":\"0\"},{\"appName\":\"IOS\",\"totalUsers\":\"4\"}]}";

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Root.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        unmarshaller.setProperty("eclipselink.media-type", "application/json");
        unmarshaller.setProperty("eclipselink.json.include-root", false);
        StreamSource json = new StreamSource(new StringReader(s));
        Root root = unmarshaller.unmarshal(json, Root.class).getValue();

        ArrayList<MiAppUsage> customer = root.appUsage;
        for(MiAppUsage miAppUsage : customer) {
            System.out.print(miAppUsage.appName);
            System.out.print(' ');
            System.out.println(miAppUsage.totalUsers);
        }
    }

}

根

我不得不介绍这个类来满足您的用例。如果您的 JSON 如下所示，我们可以消除此类:[{"appName":"ANDROID","totalUsers":"0"},{"appName":"IOS","totalUsers":"4"} ]。

package forum9924567;

import java.util.ArrayList;
import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
public class Root {

    ArrayList<MiAppUsage> appUsage;

}

MiApp 使用

package forum9924567;

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
public class MiAppUsage {

    String appName;
    int totalUsers;

}

jaxb.properties

要将 MOXy 指定为您的 JAXB 提供程序，您需要在与域类相同的包中添加一个名为 java.properties 的文件，其中包含以下条目:

javax.xml.bind.context.factory = org.eclipse.persistence.jaxb.JAXBContextFactory

输出

以下是运行演示代码的输出:

ANDROID 0
IOS 4

了解更多信息

• http://blog.bdoughan.com/2011/08/json-binding-with-eclipselink-moxy.html
• http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html