String json = {"a":"100",
"b":[{"b1":"b_value1","b2":"b_value2"},
{"b1":"b_value1","b2":"b_value2"}]，
"c":{"c1":"c_value1","c2":"c_value2"}}

public class JsonBean {
      public String a;
      public List<B> b;
      public C c;

      public static class B {
   public String b1;
   public String b2;
     }
  
     public static class C {
   public String c1;
   public String c2;
     }
}

 Gson gson = new Gson();
 java.lang.reflect.Type type = new TypeToken<JsonBean>() {}.getType();
 JsonBean jsonBean = gson.fromJson(json, type);