【Gson三】Gson解析{"data":{"IM":["MSN","QQ","Gtalk"]}}
编程技术 / houtizong 发布于 3年前 199
如何把如下简单的JSON字符串反序列化为Java的POJO对象?
{"data":{"IM":["MSN","QQ","Gtalk"]}}
下面的POJO类Model无法完成正确的解析：
import com.google.gson.Gson;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;class Model { private Map<String, Map<String, List<String>>> data; public Map<String, Map<String, List<String>>> getData() { return data; } public void setData(Map<String, Map<String, List<String>>> data) { this.data = data; }}public class ModelTest { public static void main(String[] args) { List<String> ims = new ArrayList<String>(); ims.add("MSN"); ims.add("QQ"); ims.add("Gtalk"); Map<String, List<String>> map = new HashMap<String, List<String>>(); map.put("IM", ims); Map<String, Map<String, List<String>>> dataMap = new HashMap<String, Map<String, List<String>>>(); dataMap.put("data", map); String str = new Gson().toJson(dataMap); System.out.println(str);/*{"data":{"IM":["MSN","QQ","Gtalk"]}}*/ Model m = new Gson().fromJson(str, Model.class); }}
异常信息：
Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 17at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:176)at com.google.gson.Gson.fromJson(Gson.java:803)at com.google.gson.Gson.fromJson(Gson.java:768)at com.google.gson.Gson.fromJson(Gson.java:717)at com.google.gson.Gson.fromJson(Gson.java:689)at gson.test4.ModelTest.main(ModelTest.java:35)at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.lang.reflect.Method.invoke(Method.java:606)at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)Caused by: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 17at com.google.gson.stream.JsonReader.beginArray(JsonReader.java:338)at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:172)at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:145)at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:40)at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:187)at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:145)at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93)at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172)... 10 more
如何解决这个问题？
仔细看了代码，出错是正常的事情。在代码中，str是从dataMap序列化而来，把这个由dataMap转换而来的JSON串str反序列为Model类型，出错是必然的
String str = new Gson().toJson(dataMap);Model m = new Gson().fromJson(str, Model.class)
那么Model对象序列化为JSON串的数据是什么样的呢？
{"data":{"data":{"IM":["MSN","QQ","Gtalk"]}}}
此时，解决的办法有两个：
1. 对于下面的JSON串，对应的数据结构是Map<String,Map<String,List<String>>>,直接把这个这个JSON串转成Map<String,Map<String,List<String>>>是可行的，比如如下的代码
{"data":{"IM":["MSN","QQ","Gtalk"]}} 将它转换为Map<String,Map<String,List<String>>>
import com.google.gson.Gson;import com.google.gson.reflect.TypeToken;import java.lang.reflect.Type;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;class Model { private Map<String, Map<String, List<String>>> data; public Map<String, Map<String, List<String>>> getData() { return data; } public void setData(Map<String, Map<String, List<String>>> data) { this.data = data; }}public class ModelTest { public static void main(String[] args) { List<String> ims = new ArrayList<String>(); ims.add("MSN"); ims.add("QQ"); ims.add("Gtalk"); Map<String, List<String>> map = new HashMap<String, List<String>>(); map.put("IM", ims); Map<String, Map<String, List<String>>> dataMap = new HashMap<String, Map<String, List<String>>>(); dataMap.put("data", map); String str = new Gson().toJson(dataMap); System.out.println(str);/*{"data":{"IM":["MSN","QQ","Gtalk"]}}*/ Type type = new TypeToken<Map<String, Map<String, List<String>>>>(){}.getType(); dataMap = new Gson().fromJson(str, type); ims= dataMap.get("data").get("IM"); for(int i = 0; i< ims.size(); i++) { System.out.println(ims.get(i)); } }} 请勿发布不友善或者负能量的内容。与人为善，比聪明更重要！
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