java.io.NotSerializableException thrown even when serializable is implemented

Question

I'm trying to save a map into a file but I'm getting java.io.NotSerializableException. I know this means that I have to implement Serializable to the class. The problem is that It's throwing the error even with Serializable implemented.

Code for storing:

private void storePoints(Map<String,WifiPoint> list) throws IOException{
    // store in file
    FileOutputStream fos = context.openFileOutput("points", Context.MODE_PRIVATE);
    ObjectOutputStream os = new ObjectOutputStream(fos);
    os.writeObject(list);
    os.close();
}

Wifipoint:

public class WifiPoint implements Serializable{
    private static final long serialVersionUID = 2;
    public String ssid;
    public String bssid;
    public String capabilities;
    public double latitude;
    public double longitude;
    public int level;
}

UPDATE: The real fix was: I needed to declare the WifiPoint in a separate file insted of declaring it inside another class.

Sorry, I didn't put the codes properly for anybody to get the correct answer

Please send stack trace. And check what is the concrete implementation of your `Map`. Probably it is not serializable. — AlexR, Feb 21 '13 at 13:57
no, you don't need a constructor. Look at cowls' answer (also AlexR) — Sababado, Feb 21 '13 at 13:58

score 2 · Answer 1 · answered Feb 21 '13 at 13:57

2

You're trying to serialize the Map check that the Map class you are using is Serializable

Note: A HashMap is Serializable, so switch to that if possible.

answered Feb 21 '13 at 13:57

cowls

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this fixed it. I didn't know that HashMap was an implementation of a Map and Map itself is not Serializable – thedjaney Feb 21 '13 at 14:15

score 1 · Answer 2 · answered Feb 21 '13 at 13:59

1

check that you actually implement java.io.Serializable
check that map you want to serialize also implements java.io.Serializable

answered Feb 21 '13 at 13:59

WeMakeSoftware

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score 1 · Accepted Answer · answered Feb 22 '13 at 16:57

1

I needed to declare the WifiPoint in a separate file insted of declaring it inside another class.

answered Feb 22 '13 at 16:57

thedjaney

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score 0 · Answer 4 · answered Feb 21 '13 at 14:01

0

You are passing Map object to storePoints method check whether the Map object you are passing implements Serializable. ( If you are using HashMap, TreeMap of java.util package will definitely implement Serializable. )

answered Feb 21 '13 at 14:01

Gnanasekaran Palanisamy

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score 0 · Answer 5 · edited May 23 '17 at 11:56

Check that Map doesn't implement the Serialization interface :

All Known Implementing Classes:
AbstractMap, Attributes, AuthProvider, ConcurrentHashMap, ConcurrentSkipListMap,
EnumMap, HashMap, Hashtable, IdentityHashMap, LinkedHashMap, PrinterStateReasons,             Properties, Provider, RenderingHints, SimpleBindings, TabularDataSupport, TreeMap,
UIDefaults, WeakHashMap

Source : http://docs.oracle.com/javase/6/docs/api/java/util/Map.html

you can try this : Java: Writting/Reading a Map from disk

java.io.NotSerializableException thrown even when serializable is implemented

5 Answers5