Or if you want to iterate json and parse only required ones heres what you can do:

Type type = new TypeToken<List<DataMetrics>>() {}.getType();

for(JsonElement elem : jsonArrayThatYouHave) {
   if (elem.getAsJsonObject().get("name").getAsString().equals("Client::Sync")) {
      result.add(gson.fromJson(elem, type));
   }
}

but I dont think this is actually faster than the first one because in both cases you are converting json to java functional object with parser and getting JsonArray or anything else. Taking into consideration the fact that both are Googles libs, i assume that parsing from JsonObject to some specific type with gson is way faster than from String (raw json) to the same specific type...

wayPoints is a JSON object. It contains another JSON object called ship. And ship contains a JSON array called first_type. So you should get the first_type array from the ship object, and iterate on this array.

How are you creating your JsonObject? Your code works for me. Consider this

import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
...
...
...
try{
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("keyInt", 2);
        jsonObject.addProperty("keyString", "val1");
        jsonObject.addProperty("id", "0123456");

        System.out.println("json >>> "+jsonObject);

        Map<String, Object> attributes = new HashMap<String, Object>();
        Set<Entry<String, JsonElement>> entrySet = jsonObject.entrySet();
        for(Map.Entry<String,JsonElement> entry : entrySet){
          attributes.put(entry.getKey(), jsonObject.get(entry.getKey()));
        }

        for(Map.Entry<String,Object> att : attributes.entrySet()){
            System.out.println("key >>> "+att.getKey());
            System.out.println("val >>> "+att.getValue());
            } 
    }
    catch (Exception ex){
        System.out.println(ex);
    }

And it is working fine. Now I am interested in knowing how you created that JSON of yours?

You can also try this (JSONObject)

import org.json.JSONObject;
...
...
...
try{
        JSONObject jsonObject = new JSONObject("{\"keyInt\":2,\"keyString\":\"val1\",\"id\":\"0123456\"}");
        System.out.println("JSON :: "+jsonObject.toString());

        Iterator<String> it  =  jsonObject.keys();
         while( it.hasNext() ){
             String key = it.next();
             System.out.println("Key:: !!! >>> "+key);
             Object value = jsonObject.get(key);
             System.out.println("Value Type "+value.getClass().getName());
            }
    }
    catch (Exception ex){
        System.out.println(ex);
    }

Suppose class Name for Json Model is Example.

import com.google.gson.annotations.SerializedName;
import java.util.List;
public class Example {

    @SerializedName("recordsTotal")
    private Integer recordsTotal;
    @SerializedName("data")
    private List<Datum> data = null;

    public Integer getRecordsTotal() {
        return recordsTotal;
    }

    public void setRecordsTotal(Integer recordsTotal) {
        this.recordsTotal = recordsTotal;
    }

    public List<Datum> getData() {
        return data;
    }

    public void setData(List<Datum> data) {
        this.data = data;
    }

}

And suppose List of Data class name is Datum :-

import com.google.gson.annotations.SerializedName;
import java.util.List;
public class Datum {

    @SerializedName("part_number")

    private String partNumber;
    @SerializedName("part_type")

    private String partType;
    @SerializedName("id")

    private Integer id;
    @SerializedName("manufacturers")

    private List<String> manufacturers = null;

    public String getPartNumber() {
        return partNumber;
    }

    public void setPartNumber(String partNumber) {
        this.partNumber = partNumber;
    }

    public String getPartType() {
        return partType;
    }

    public void setPartType(String partType) {
        this.partType = partType;
    }

    public Integer getId() {
        return id;
    }

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

    public List<String> getManufacturers() {
        return manufacturers;
    }

    public void setManufacturers(List<String> manufacturers) {
        this.manufacturers = manufacturers;
    }

}

And then through Gson library we can convert json to java Model :

Example example = new Gson().fromJson(jsonString, new TypeToken<Example>() {}.getType());

Now we can get list of data though example model :-

List<Datum>  dataList = example.getData();

From dataList you can traverse and get all info.

If partNmber List we need then we can get in this way :-

 List<String> partNumberList = new ArrayList<>();
 for (Datum data : dataList) {
       partNumberList.add(data.getPartNumber());
  }