Question

我有一个JSON文件：

{
"settings": {
    "header": {
        "id": "240A64CDC43F",
        "filename": "network",
        "sequence": "0",
        "last_modified": "2015-04-21T16:33",
        "JSON_file_version": "2.1"
    },
    "data": {
        "engine_config": {
            "bed_name": "IdealTempCDC43F",
            "provisioned": "false",
            "connected": "false",
            "IP_address": "192.168.10.1",
            "connection_error": "None"
        },
        "networks": {
            "available": "7",
            "SSIDs": {
                "wireless_1": {
                    "SSID": "$$ASI_WIFI$$",
                    "mac_address": "A0:EC:F9:11:35:04",
                    "channel": "11",
                    "RSSI": "-64dBm",
                    "security": "true",
                    "security_type": "WPA"
                },
                "wireless_2": {
                    "SSID": "$$ASI_GUEST$$",
                    "mac_address": "A0:EC:F9:11:35:02",
                    "channel": "11",
                    "RSSI": "-65dBm",
                    "security": "true",
                    "security_type": "WPA"
                }
            }
        }
    }
}
}

为了解析这个json我正在使用它：

HttpResponse response = client.execute(request); 
String strResponse = response.toString();
parseJSON(strResponse);

和

public void parseJSON(String jsonString) {
  Gson gsonParser = new Gson();
  ProveQuerySetting gsonResponse = new ProveQuerySetting();
  Type collectionType = new TypeToken<Collection<ProveQuerySetting>>() {
  }.getType();
  gsonResponse = gsonParser.fromJson(jsonString, collectionType);
  String str = gsonParser.toJson(gsonResponse);
  System.out.println(" final json " + str);
}

但我得到了这个例外：

04-21 07:08:13.864: W/System.err(4187): com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 1 path $
04-21 07:08:13.864: W/System.err(4187): com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 1 path $
04-21 07:08:13.865: W/System.err(4187):     at com.google.gson.Gson.fromJson(Gson.java:822)
04-21 07:08:13.865: W/System.err(4187):     at com.google.gson.Gson.fromJson(Gson.java:775)
04-21 07:08:13.865: W/System.err(4187):     at com.google.gson.Gson.fromJson(Gson.java:724)
04-21 07:08:13.865: W/System.err(4187):     at com.easi.main.network.NetworkCom.parseJSON(NetworkCom.java:127)
04-21 07:08:13.865: W/System.err(4187):     at com.easi.main.network.NetworkCom.sendFirst(NetworkCom.java:50)
04-21 07:08:13.865: W/System.err(4187):     at com.easi.main.setting.ConnectToBox$MyAsyncTask.doInBackground(ConnectToBox.java:89)
04-21 07:08:13.865: W/System.err(4187):     at com.easi.main.setting.ConnectToBox$MyAsyncTask.doInBackground(ConnectToBox.java:1)
04-21 07:08:13.865: W/System.err(4187):     at android.os.AsyncTask$2.call(AsyncTask.java:288)
04-21 07:08:13.865: W/System.err(4187):     at java.util.concurrent.FutureTask.run(FutureTask.java:237)
04-21 07:08:13.865: W/System.err(4187):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
04-21 07:08:13.865: W/System.err(4187):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
04-21 07:08:13.865: W/System.err(4187):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
04-21 07:08:13.865: W/System.err(4187):     at java.lang.Thread.run(Thread.java:818)
04-21 07:08:13.865: W/System.err(4187): Caused by: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 1 path $
04-21 07:08:13.865: W/System.err(4187):     at com.google.gson.stream.JsonReader.beginArray(JsonReader.java:350)
04-21 07:08:13.866: W/System.err(4187):     at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:79)
04-21 07:08:13.866: W/System.err(4187):     at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:60)
04-21 07:08:13.866: W/System.err(4187):     at com.google.gson.Gson.fromJson(Gson.java:810)
04-21 07:08:13.866: W/System.err(4187):     ... 12 more

这是我的POJO课程：

public class ProveQuerySetting {
  ProvQueryData provEngnData;
  ProvQueryHeader provEngnhHeader;

  public ProvQueryData getProvEngnData() {
    return provEngnData;
  }

  public void setProvEngnData(ProvQueryData provEngnData) {
    this.provEngnData = provEngnData;
  }

  public ProvQueryHeader getProvEngnhHeader() {
    return provEngnhHeader;
  }

  public void setProvEngnhHeader(ProvQueryHeader provEngnhHeader) {
    this.provEngnhHeader = provEngnhHeader;
  }
}

为什么我会收到此异常？

Answer 1

好的，所以你试图使用默认的Gson。大！默认的Gson很聪明，但不是那么聪明。您必须将类设计为完全匹配您要获取的json的格式，或者如果您不想设计自定义反序列化器，则使用@SerializedName注释。当我说完全匹配时，我的意思是，字段名称必须与序列化Gson完全相同，无论是在字段名称还是注释中。

我创建了以下POJO（包括您的POJO，带有修改的字段名称）。为简洁起见，我没有包含getters / setter：

public class ProvEngineConfig {
  private String bed_name;
  private String provisioned;
  private String connected;
  private String IP_Address;
  private String connection_error;
}

public class ProvNetworks {
  private String available;
  private Map<String, ProvSSID> SSIDs;  // Notice this is a map
}

public class ProveQuerySetting {
  ProvQueryData data;
  ProvQueryHeader header;
}

public class ProvQueryData {
  ProvEngineConfig engine_config;
  ProvNetworks networks;
}

public class ProvQueryHeader {
  String id;
  String filename;
  String sequence;
  String last_modified;
  String JSON_file_version;
}

public class ProvSSID {
  String SSID;
  String mac_address;
  String channel;
  String RSSI;
  String security;
  String security_type;
}

同样，您是否看到字段名称完全与JSON中的字段名称相同？请注意，在ProvNetworks中，我正在使用地图，因为您提供的JSON是无线名称的地图，以完全匹配SSID对象。

我的POJO设置如下，请注意您提供的JSON不是Collection的查询设置，实际上是Map<String, ProvQuerySetting>，您可以从单词"settings"映射到引擎配置对象。所以我这样解析它：

public static void parseJSON(String jsonString) {
  Gson gsonParser = new Gson();
  Map<String, ProveQuerySetting> gsonResponse; // You don't need to do new here
  Type collectionType = new TypeToken<Map<String, ProveQuerySetting>>() {}.getType();
  gsonResponse = gsonParser.fromJson(jsonString, collectionType);

  String str = gsonParser.toJson(gsonResponse);
  System.out.println(" final json " + str);
}

输出：

final json {"settings":{"data":{"engine_config":{"bed_name":"IdealTempCDC43F","provisioned":"false","connected":"false","connection_error":"None"},"networks":{"available":"7","SSIDs":{"wireless_1":{"SSID":"$$ASI_WIFI$$","mac_address":"A0:EC:F9:11:35:04","channel":"11","RSSI":"-64dBm","security":"true","security_type":"WPA"},"wireless_2":{"SSID":"$$ASI_GUEST$$","mac_address":"A0:EC:F9:11:35:02","channel":"11","RSSI":"-65dBm","security":"true","security_type":"WPA"}}}},"header":{"id":"240A64CDC43F","filename":"network","sequence":"0","last_modified":"2015-04-21T16:33","JSON_file_version":"2.1"}}}

总结：

您需要：

完全匹配您的POJO和字段名称/带注释的字段名称以匹配JSON
编写您自己的自定义反序列化程序，如JsonReader

Answer 2

Gson API很好，但我发现另一个API Jackson更强大且用户友好。需要两个jar文件jackson-core-asl-1.8.5和jackson-mapper-asl-1.8.5 然后

ObjectMapper mapper = new ObjectMapper();
    MAinpojo object = null;
    System.out.println("json string  "+jsonString.trim());
    try {
         object = mapper.readValue(new URL("http://192.168.xx.x/pmmm-zzzz"), MAinpojo.class);
    } catch (JsonParseException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (JsonMappingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

最后但并非最不重要的是关心你的POJO课程。

1.字段名称应该相同。

2.如果在某个字段中出现无法识别的异常，请使用此类注释

  @JsonIgnoreProperties(ignoreUnknown=true)
public class MAinpojo {

     @JsonProperty("settings") 
     ProveQuerySetting settings;


     @JsonProperty("settings") 
     public ProveQuerySetting getSettings() {
        return settings;
    }

    public void setSettings(ProveQuerySetting settings) {
        this.settings = settings;
    }

}

在所有字段之上，可能会抛出异常。

为什么我得到一个JsonSyntaxException：预期BEGIN_ARRAY但是STRING在这里？

2 个答案:

总结：