cant serialize my class Java

Question

It seems like I can't serialize my class called "Ban":

class Ban implements Serializable{
        /**
         * 
         */
        transient Date start;
        transient Date end;
        String explination;
        String from;
        public Ban(Date s, Date e, String ex, String f){
            start = s;
            end = e;
            explination = ex;
            from = f;
        }
    }

When I try to print this with a objectoutputstream it gives me an ERROR... Could you please help me by serializing this class? BTW: What does transient mean?

well it is bukkit but this should do it:

[SEVERE] java.io.NotSerializableException: me.bubblegumsoldier.Ban.Main
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectOutputStream.writeObject0(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectOutputStream.defaultWriteFields(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectOutputStream.writeSerialData(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectOutputStream.writeObject0(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectOutputStream.writeObject(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.util.HashMap.writeObject(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
2013-04-03 19:30:30 [SEVERE]    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.lang.reflect.Method.invoke(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectStreamClass.invokeWriteObject(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectOutputStream.writeSerialData(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectOutputStream.writeObject0(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at java.io.ObjectOutputStream.writeObject(Unknown Source)
2013-04-03 19:30:30 [SEVERE]    at me.bubblegumsoldier.Ban.Main.save(Main.java:113)
2013-04-03 19:30:30 [SEVERE]    at me.bubblegumsoldier.Ban.Main.onDisable(Main.java:247)
2013-04-03 19:30:30 [SEVERE]    at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:219)
2013-04-03 19:30:30 [SEVERE]    at org.bukkit.plugin.java.JavaPluginLoader.disablePlugin(JavaPluginLoader.java:481)
2013-04-03 19:30:30 [SEVERE]    at org.bukkit.plugin.SimplePluginManager.disablePlugin(SimplePluginManager.java:400)
2013-04-03 19:30:30 [SEVERE]    at org.bukkit.plugin.SimplePluginManager.disablePlugins(SimplePluginManager.java:393)
2013-04-03 19:30:30 [SEVERE]    at org.bukkit.craftbukkit.v1_5_R2.CraftServer.disablePlugins(CraftServer.java:277)
2013-04-03 19:30:30 [SEVERE]    at net.minecraft.server.v1_5_R2.MinecraftServer.stop(MinecraftServer.java:331)
2013-04-03 19:30:30 [SEVERE]    at net.minecraft.server.v1_5_R2.MinecraftServer.run(MinecraftServer.java:438)
2013-04-03 19:30:30 [SEVERE]    at net.minecraft.server.v1_5_R2.ThreadServerApplication.run(SourceFile:573)

My saving code looks like this:

The variable:

public static HashMap<String, Ban> banned = new HashMap<String, Ban>();

The saving part:

ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(file));
oos.writeObject(banned);
oos.flush();
oos.close();

What error does it give you? `transient` means that the property should not be serialized. — Vivin Paliath, Apr 03 '13 at 17:22
What is the error message? Copy and paste it into your question. You probably need to add a public default constructor. — Thorn, Apr 03 '13 at 17:22
for transient variable see this:- http://stackoverflow.com/questions/5245600/what-does-the-keyword-transient-means-in-java — Avinesh, Apr 03 '13 at 17:25
`transient` definition can be found here [link](http://stackoverflow.com/questions/5245600/what-does-the-keyword-transient-means-in-java) — Khanh Tran, Apr 03 '13 at 17:26

score 2 · Accepted Answer · answered Apr 03 '13 at 17:44

It seems you have defined Ban as a non-static inner class of another class called Main:

public class Main {

    class Ban {
        ...
    }
}

This means that every Ban instance has an implicit reference to its outer Main instance. The code above is similar to the following one:

public class Main {
    static class Ban {
        private Main main;
    }
}

or public class Main { }

class Ban {
    private Main main;
}

So when you serialize a Ban, you're also serializing this implicit instance, which is not serializable, hence the exception.

Make Ban a top-level class, or a static inner class.

Thorn · Answer 2 · 2013-04-03T17:37:01.193

There is nothing wrong with the Ban class as posted. Maybe the error was produced by your class including a Main field variable that is not serializable. But the code posted in the question can be serialized; We can run this:

public class Ban implements Serializable {

  transient Date start;
  transient Date end;
  String explination;
  String from;

  public Ban(Date s, Date e, String ex, String f) {
     start = s;
     end = e;
     explination = ex;
     from = f;
  }

  public String toString() {
     return "Ban{" + "start=" + start + ", end=" + end + ", explination=" + explination + ", from=" + from + '}';
  }

  public static void main(String[] args) throws IOException, ClassNotFoundException {
     Ban x = new Ban(new Date(), new Date(), "Transient means do not serialize.", "Thorn");
     File f = new File("test.out");
     ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(f));
     out.writeObject(x);
     out.close();

     ObjectInputStream in = new ObjectInputStream(new FileInputStream(f));
     Ban fromFile = (Ban) in.readObject();
     System.out.println(fromFile);
     in.close();
  }

}

The output produced is:

 Ban{start=null, end=null, explination=Transient means do not serialize., from=Thorn}

Note that the output has both dates as null even though I gave them values. A transient value is not serialized.

I ran the code without an error. If I got the same exception you did then the output pasted into my answer would not have been produced. Try copying and pasting my code and running it. — Thorn, Apr 03 '13 at 17:41

score 0 · Answer 3 · edited May 23 '17 at 10:28

0

The transient keyword in Java is used to indicate that a field should not be serialized. See this post for more details Why does Java have transient fields?

Without your error cpde we cannot assist you

edited May 23 '17 at 10:28

Community

1
1

answered Apr 03 '13 at 17:25

evgenyl

7,837
2
27
32

score 0 · Answer 4 · answered Apr 03 '13 at 17:28

0

transient variables cannot be serialized.

answered Apr 03 '13 at 17:28

PranitG

121
8

Can you clarify how/why this is? – Stuart M Apr 03 '13 at 17:46
transient is a Java keyword specifically created to exclude variables from serialization. Remove it and you can potentially serialize a variable. There are many beginner introductions to the topic try the SCJP book by Bates and Sierra – Crowie Sep 03 '13 at 08:50

score 0 · Answer 5 · answered Apr 03 '13 at 17:45

0

The transient fields are not serialized, they will be null after reading from a stream. The error seems to come from an inner class named Main which is missing in your code example and not implement Serializable!

answered Apr 03 '13 at 17:45

Arne Burmeister

20,046
8
53
94

cant serialize my class Java

5 Answers5