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Web App HashMap Serilization

Craig Worsell

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posted 12 years ago

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Hi all, I am trying to create a test login jsp/servlet app. For now I want to create a HashMap to store the username and passwords (I would not do this in real life) and then serialize the HashMap.

I would like to open the serliized object to search when the user logs back on and when a new one is created to check the username is not already in use.

I have written a java class for the servlet to instantiate with methods to do both the verification and creation but the serialization part does not seem to work.

My question is this: Am I able to serialize and de-serialize a HashMap in a web app?
This is my current code for doing so:

public String createUser(String uName, String pWord) {
        HashMap hm = null;
        try {
            FileInputStream fis = new FileInputStream("hm.ser");
            ObjectInputStream ois = new ObjectInputStream(fis);
            hm = (HashMap) ois.readObject();
            if (hm.containsKey(uName))
                return "User name " + uName + " already exsists, please choose another."; 
            hm.put(uName, pWord);
        } catch (ClassNotFoundException cnf) {
            hm = new HashMap();
            hm.put(uName, pWord);
        } catch (IOException e) {
            return "There was an error, read class, please try again.";
        } finally {
            try {
                FileOutputStream fos = new FileOutputStream("hm.ser");
                ObjectOutputStream oos = new ObjectOutputStream(fos);
                oos.writeObject(hm);
                oos.close();
            } catch (IOException e){
                return "There was an error, cannot serialize, please try again.";
            }
        }
        return "The user " + uName + " has been created!";
    }

Many Thanks.

Rob Spoor

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posted 12 years ago

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Although it's not the best way (but you already know that), it's definitely possible to serialize and de-serialize a HashMap, as long as its contents are also serializable (which Strings are). However, you need to add some synchronization to ensure only one request can access the file at a time, or you risk your data getting inaccurate or even corrupted.

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Craig Worsell

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posted 12 years ago

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you need to add some synchronization to ensure only one request can access the file at a time

I thought I'd get the actual serilization to work before adding this, but thank you.

Should the code I posted work for my intended purpose from what you can see?
Below is what should call it which is in my servlet:

Thanks.

Rob Spoor

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posted 12 years ago

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You never close the FileInputStream.

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Craig Worsell

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posted 12 years ago

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Thanks Rob. I have fixed that but it is still not serializing the object it I am getting the below messages:

WARNING: Internal error flushing the buffer in release()
WARNING: StandardWrapperValve[jsp]: PWC1406: Servlet.service() for servlet jsp threw exception
java.io.IOException: Stream closed

Although I am not closing the steam...
Any thoughts?

Thanks again.

Ragavendran Baskaran

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posted 12 years ago

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Try closing the FileOutputStream object.

Rob Spoor

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posted 12 years ago

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Craig Worsell wrote:UserValidation uv = new UserValidation(); PrintWriter out = response.getWriter(); try { out.println("<html>"); out.println("<head>"); out.println("<title>Servlet CreateAccount</title>"); out.println("</head>"); out.println("<body>"); out.println("<h1>" + uv.createUser(request.getParameter("uName"), request.getParameter("pWord")) + "</h1>"); out.println("</body>"); out.println("</html>"); } finally { out.close(); }

Don't close out. That's what's causing the latest exception.

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Craig Worsell

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posted 12 years ago

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Thanks both. I also worked out that I needed to put the full path to save the .ser file, and as I am running off the localhost I had to put the path for my local drive (C:\) where my project is saved. However if this was a live web app how would I save the .ser file to the server as I tried http://localhost:8080/WebApplication1/... but this did not work?

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