Databases
StackOverflow2013
Postsdbo
POTrouble with Gson serializing an ArrayList of POJO's
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POTrouble with Gson serializing an ArrayList of POJO's
    primarykey
    data
    text
    <p>I had been planning on using simpleXML for my serialization needs, but figured I would try JSON out, to learn something new. </p> <p>This is the code I am using to try and serialize an ArrayList of test POJO's using Gson 1.7.1. </p> <p>Note: I removed the Reader/Writers for a String "s" to simplify the code.</p> <pre><code>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&lt;TestObject&gt; list = Collections.synchronizedList(new ArrayList&lt;TestObject&gt;() ); list.add(new TestObject()); list.add(new TestObject()); s = gson.toJson(list, ArrayList.class); System.out.println(s); //Eat Serial List&lt;TestObject&gt; list2 = Collections.synchronizedList(gson.fromJson(s, ArrayList.class) ); System.out.println(list2.get(0) ); System.out.println(list2.get(1) ); } } </code></pre> <p>Here is the output I get:</p> <pre><code>[{"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 </code></pre> <p>To my newbie eyes this looks correct. Only, the DeSerialized list of objects contains basic Objects, rather then the TestObject's I serialized. Can anyone please explain to me what, if anything, I can do to make this work?</p> <p><strong>EDIT:</strong></p> <p>Corrected to test: Thanks to ColinD</p> <pre><code>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&lt;List&lt;TestObject&gt;&gt;(){}.getType(); //Make Serial Writer osWriter = new OutputStreamWriter( new FileOutputStream(fileName)); List&lt;TestObject&gt; list = Collections.synchronizedList(new ArrayList&lt;TestObject&gt;() ); 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&lt;TestObject&gt; list2 = Collections.synchronizedList( (List&lt;TestObject&gt;)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 ---"); } } </code></pre> <p>output:</p> <pre><code>--- 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 --- </code></pre> <p><strong>EDIT2:</strong></p> <p>I honestly don't know why, but when I replaced the simple String[] embedded in my TestObject with an ArrayList, it started serializing correctly.</p> <pre><code>--- 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 --- </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USRogueDeus
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    3. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POTrouble with Gson serializing an ArrayList of POJO's
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POTrouble with Gson serializing an ArrayList of POJO's
      1. USNimit Pattanasri
      1. VTFavorite
    3. VO
      singulars
      1. POTrouble with Gson serializing an ArrayList of POJO's
      1. USaustin
      1. VTFavorite
    1. COside note: Get rid of the Collections.synchronizedList() calls. You have a single-thread scenario, these calls only add overhead, nothing else
      singulars
      1. POTrouble with Gson serializing an ArrayList of POJO's
      1. USSean Patrick Floyd
    2. COYou are correct. They are there to make sure I can get it working. Once its working, I will remove them. This is purely for educational reasons. Once I get a good idea of Json serialization I will begin building for actual use.
      singulars
      1. POTrouble with Gson serializing an ArrayList of POJO's
      1. USRogueDeus
    3. COHaving said that, can anyone point me to where I can figure out how to get the Object embedded array to deserialize with a TypeToken?
      singulars
      1. POTrouble with Gson serializing an ArrayList of POJO's
      1. USRogueDeus
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload