Topic: How do I serialize a hashtable?

How do I serialize a hashtable?

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Posted By: Anonymous
Posted On: Thursday, June 14, 2001 12:36 PM

I have a method for serializing a hashtable. _cache is the hashtable, and _cachefile is the name of the file to serialize to (both are global variables in a servlet class). Here is my method: ObjectOutputStream os = new ObjectOutputStream(new FileOutputStream(_cachefile)); os.writeObject(_cache); os.close(); Am I missing something? When I call this method, my hashtable is serializing, but none of the data is saved. Every single key and value in the hashtable is a String (which is serializable), but when I go to load the object, the hashtable I load is empty! Thanks for the help, ~Matt More>>

I have a method for serializing a hashtable. _cache is the hashtable, and _cachefile is the name of the file to serialize to (both are global variables in a servlet class).

Here is my method:

			

			ObjectOutputStream os = new ObjectOutputStream(new FileOutputStream(_cachefile));
			

			

			os.writeObject(_cache);
			

			

			os.close();

Am I missing something? When I call this method, my hashtable is serializing, but none of the data is saved. Every single key and value in the hashtable is a String (which is serializable), but when I go to load the object, the hashtable I load is empty!

Thanks for the help,

~Matt

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Re: How do I serialize a hashtable?

Posted By: Tim_Rohaly
Posted On: Thursday, June 14, 2001 01:27 PM

Works for me - I don't know what you're doing wrong,
but it is your code which is bad.
Here is my test code:


import java.io.*;
import java.util.*;

public class hash {

    public static void main(String[] args) throws Exception {
        // create hashtable
        Hashtable numbers = new Hashtable();
        numbers.put("one",   new Integer(1));
        numbers.put("two",   new Integer(2));
        numbers.put("three", new Integer(3));

        // write out hashtable
        ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("hash.ser"));
        out.writeObject(numbers);
        out.flush();
        out.close();

        // read in hashtable
        ObjectInputStream in = new ObjectInputStream(new FileInputStream("hash.ser"));
        Hashtable table = (Hashtable) in.readObject();
        in.close();

        Enumeration keys = table.keys();
        System.out.println("Deserialized Hashtable contains:");
        while (keys.hasMoreElements()) {
            String s = (String) keys.nextElement();
            System.out.println("    key=" + s +
                               "	value=" + (Integer) table.get(s));
        }
    }
}

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