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POSending the same objects with different fields over an object serialized stream
 

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  1. POSending the same objects with different fields over an object serialized stream
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    <p>I have a client/server program, and I'm sending objects through <code>ObjectOutputStream</code> via <code>writeObject()</code> and <code>readObject()</code>. </p> <p>The object I'm sending is class consisting of a couple of fields, and another object inside (let's call the outer object <code>Wrapper</code> and the inner <code>Inner</code>. Both the custom objects implement <code>serializable</code>.</p> <p>The first time I send the <code>Wrapper</code> over, everything works flawlessly. Everything stored in both <code>Wrapper</code>, <code>Inner</code> and all the fields serialize and deserialize without problems.</p> <p>However, when the client then modifies the <code>Inner</code> class, puts it in the <code>Wrapper</code>, and sends it one more time, the <code>Inner</code> instance received by the server, is identical to the one received the first time around.</p> <p>My client: </p> <pre class="lang-java prettyprint-override"><code>Inner inner = new Inner(); inner.setValue("value"); ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream()); out.writeObject(new Wrapper(inner)); </code></pre> <p>Server:</p> <pre class="lang-java prettyprint-override"><code>ObjectInputStream in = new ObjectInputStream(clientSocket.getInputStream()); Wrapper wrapper = (Wrapper) in.readObject(); String value = wrapper.getInner().getValue(); </code></pre> <p>Client then modifies the <code>Inner</code> class (same instance as before) with a DIFFERENT string (ie. containing other letters then the first one):</p> <pre class="lang-java prettyprint-override"><code>inner.setValue("newValue"); out.writeObject(new Wrapper(inner)); </code></pre> <p>However, when I look at the <code>inner.getValue()</code> on the server, it has not changed and is still equal to <code>"value"</code>.</p> <p>I solved this, by making a hard copy of the inner class, before sending it over:</p> <pre class="lang-java prettyprint-override"><code>Inner newInner = new Inner(); newInner.setValue("newValue"); out.writeObject(new Wrapper(newInner)); </code></pre> <p>The new value now is updated as it should.</p> <p>Why does serialization work this way?</p>
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