Gson序列化POJO的ArrayList的麻烦

Question

我一直在计划使用simpleXML来满足我的序列化需求,但我想我会尝试使用JSON来学习新的东西.

这是我用来尝试使用Gson 1.7.1序列化测试POJO的ArrayList的代码.

注意:我删除了字符串"s"的读/写器以简化代码.

package test;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import com.google.gson.Gson;

public class TestGsonSerialDeserialList {
    public static void main(String[] args) throws IOException{
        Gson gson = new Gson();

        //Make Serial 
        String s;
        List<TestObject> list = Collections.synchronizedList(new ArrayList<TestObject>() );
        list.add(new TestObject());
        list.add(new TestObject());

        s = gson.toJson(list, ArrayList.class);
        System.out.println(s);

        //Eat Serial
        List<TestObject> list2 = Collections.synchronizedList(gson.fromJson(s, ArrayList.class) );
        System.out.println(list2.get(0) );
        System.out.println(list2.get(1) );
    }
}

这是我得到的输出:

[{"objectID":1,"i1":12345,"name":"abcdefg","s":["a","b","c"]},{"objectID":2,"i1":12345,"name":"abcdefg","s":["a","b","c"]}]
java.lang.Object@5c74c3aa
java.lang.Object@75d9fd51

对我的新手来说,这看起来是正确的.只有DeSerialized对象列表包含基本对象,而不是我序列化的TestObject.任何人都可以向我解释一下,如果有的话,我可以做些什么来使这项工作？

编辑:

更正测试:感谢ColinD

package test;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.Writer;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

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

public class TestGsonSerialDeserialList {
    public static void main(String[] args) throws IOException{
        System.out.println("--- Serialize / Deserialize Started ---");
        String fileName = "json\\testList.json";

        Gson gson = new Gson();
        Type listOfTestObject = new TypeToken<List<TestObject>>(){}.getType();

        //Make Serial 
        Writer osWriter = new OutputStreamWriter( new FileOutputStream(fileName));
        List<TestObject> list = Collections.synchronizedList(new ArrayList<TestObject>() );
        list.add(new TestObject());
        list.add(new TestObject());
        list.add(new TestObject());
        list.add(new TestObject());
        gson.toJson(list, osWriter);
        osWriter.close();


        //Eat Serial
        Reader isReader = new InputStreamReader( new FileInputStream((fileName) ) );
        List<TestObject> list2 = Collections.synchronizedList(
            (List<TestObject>)gson.fromJson(isReader, listOfTestObject) 
        );
        isReader.close();
        System.out.println(list2.get(0) );
        System.out.println(list2.get(1) );
        System.out.println(list2.get(2) );
        System.out.println(list2.get(3) );
        System.out.println("--- Serialize / Deserialize Ended ---");
    }
}

输出:

--- Serialize / Deserialize Started ---
ID#: 1, i1: 12345, name: abcdefg, s[]: [Ljava.lang.String;@95c083
ID#: 2, i1: 12345, name: abcdefg, s[]: [Ljava.lang.String;@6791d8c1
ID#: 3, i1: 12345, name: abcdefg, s[]: [Ljava.lang.String;@182d9c06
ID#: 4, i1: 12345, name: abcdefg, s[]: [Ljava.lang.String;@5a5e5a50
--- Serialize / Deserialize Ended ---

EDIT2:

老实说,我不知道为什么,但当我用一个ArrayList替换我的TestObject中嵌入的简单String []时,它开始正确序列化.

--- Serialize / Deserialize Started ---
ID#: 1, i1: 12345, name: abcdefg, s[]: [a, b, c]
ID#: 2, i1: 12345, name: abcdefg, s[]: [a, b, c]
ID#: 3, i1: 12345, name: abcdefg, s[]: [a, b, c]
ID#: 4, i1: 12345, name: abcdefg, s[]: [a, b, c]
--- Serialize / Deserialize Ended ---

Answer 1

您需要提供有关List您正在使用的特定泛型类型(或您使用它的任何泛型类型)的Gson信息.特别是在反序列化JSON时,它需要该信息能够确定它应该将每个数组元素反序列化的对象类型.

Type listOfTestObject = new TypeToken<List<TestObject>>(){}.getType();
String s = gson.toJson(list, listOfTestObject);
List<TestObject> list2 = gson.fromJson(s, listOfTestObject);

这在Gson用户指南中有记录.