Java 如何将类> 传递给方法？

Question

我得到 Json 字符串，我想创建将 Json 字符串转换为对象的通用方法。我创建对象

public class ResponseMessage<T> {

    private T result;
    private ResultCode resultCode;
    private String details;

    public ResponseMessage(T result, ResultCode resultCode, String details) {
        this.result = result;
        this.resultCode = resultCode;
        this.details = details;
    }

    public T getResult() {
        return result;
    }

    public void setResult(T result) {
        this.result = result;
    }

    public ResultCode getResultCode() {
        return resultCode;
    }

    public void setResultCode(ResultCode resultCode) {
        this.resultCode = resultCode;
    }

    public String getDetails() {
        return details;
    }

    public void setDetails(String details) {
        this.details = details;
    }
}

我想将泛型类型传递给我的类并返回对象。但我不知道该怎么做。我创建类 Converter

public class Converter {
    private static Converter instance;
    private Gson gson = new Gson();

    public static Converter me() {
        if (instance == null) {
            instance = new Converter();
        }
        return instance;
    }

    public <T> T getModel(String jsonStr, Class<T> type) {
        T t = gson.fromJson(jsonStr, type);
        return t;
    }

    public <T> List<T> getModelList(String jsonStr, Class<T[]> clazz) {
        T[] yourClassList = new Gson().fromJson(jsonStr, clazz);
        return Arrays.asList(yourClassList);
    }
}

我试过了

String s = RESTUtil.doPost(url, formData);
ResponseMessage<ArrayList<CallDetail>> model = Converter.me().getModel(s, ResponseMessage<ArrayList<CallDetail>>.class);

但这是错误的。 s - 它是 Json 字符串。

ResponseMessage<ArrayList<CallDetail>>.class - type(I don't know how pass it)

Answer 1

我创建了一个 SSCE ，这本质上是一个带有解决方案的简短的自包含示例。请注意内联评论。

请注意，我们已将 MyClass 的边界限制为扩展 List 类。

package com.so34985191;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

import java.lang.reflect.Type;
import java.util.Arrays;
import java.util.List;

/**
 * Solution for SO question 34985191
 */
public class GsonTest {
  public static void main(String args[]) {
    Converter converter = new Converter();

    List<Integer> sampleList1 = Arrays.asList(new Integer[] {1, 2, 3});
    List<Integer> sampleList2 = Arrays.asList(new Integer[] {5, 6, 7});

    @SuppressWarnings({"rawtypes"})
    MyClass[] test = {
        new MyClass<List<Integer>, Integer>(sampleList1),
        new MyClass<List<Integer>, Integer>(sampleList2)};

    Gson gs = new Gson();
    String jsonEncodedString = gs.toJson(test);

    // Example where the type is provided to the getModelList method
    Type listType = new TypeToken<MyClass<List<Integer>, Integer>[]>() {}.getType();
    System.out.println(converter.getModelList(jsonEncodedString, listType));

    // Trying with another example.
    Type nameType = new TypeToken<Test[]>() {}.getType();
    System.out.println(converter.getModelList(
        gs.toJson(new Test[] {new Test("Java"), new Test("Scala")}), nameType));
  }

  /**
   *
   * Utility class to convert a json encoded strings to respective types.
   */
  public static class Converter {
    /**
     * Converts the encoded json string to respective type depeding on the provided type parameter
     * @param jsonStr the string to be decoded.
     * @param type the type used for conversion
     * @return the decoded list
     */
    public <T> List<T> getModelList(String jsonStr, Type type) {
      T[] yourClassList = new Gson().fromJson(jsonStr, type);
      return Arrays.asList(yourClassList);
    }
  }

  /**
   * Container for a list of ids.
   * @param <E>
   */
  public static class MyClass<T extends List<E>, E> {
    private final T ids;

    public MyClass(T ids) {
      this.ids = ids;
    }

    public T getId() {
      return this.ids;
    }

    @Override
    public String toString() {
      return this.ids.toString();
    }
  }

  /**
   * A sample wrapper over string.
   */
  public static class Test {
    private final String name;

    public Test(String name) {
      this.name = name;
    }

    public String getName() {
      return this.name;
    }

    @Override
    public String toString() {
      return this.name;
    }
  }
}