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PODeserialize a final list attribute
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  1. PODeserialize a final list attribute
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    copied!<p>Suppose we have a class Test like:</p> <pre><code>public class Test { private final String name; private final List&lt;String&gt; list = new ArrayList&lt;&gt;(); public Test(String name) { this.name = name; } void add(String s) { list.add(s); } void print() { System.out.println("name: " + name); for (String s : list) { System.out.println(" - " + s); } } } </code></pre> <p>Without XSteam the invariant</p> <pre><code>this.list != null </code></pre> <p>holds every time.</p> <p>But if we look in the 4th test in</p> <pre><code>public static void main(String[] args) { final XStream xstream = new XStream(); xstream.alias("test", Test.class); // Serialize final Test test1 = new Test("XYZ"); test1.add("One"); test1.add("Two"); //@formatter:off /* name: XYZ * - One * - Two */ //@formatter:on test1.print(); //@formatter:off /* &lt;test&gt; * &lt;name&gt;XYZ&lt;/name&gt; * &lt;list&gt; * &lt;string&gt;One&lt;/string&gt; * &lt;string&gt;Two&lt;/string&gt; * &lt;/list&gt; * &lt;/test&gt; */ //@formatter:on System.out.println(xstream.toXML(test1)); // Deserialize with one list entry final String xmlTest2 = "&lt;test&gt;&lt;name&gt;XYZ&lt;/name&gt;&lt;list&gt;&lt;string&gt;One&lt;/string&gt;&lt;/list&gt;&lt;/test&gt;"; final Test test2 = (Test) xstream.fromXML(xmlTest2); //@formatter:off /* &lt;test&gt; * &lt;name&gt;XYZ&lt;/name&gt; * &lt;list&gt; * &lt;string&gt;One&lt;/string&gt; * &lt;/list&gt; * &lt;/test&gt; */ //@formatter:on test2.print(); // Deserialize with empty list final String xmlTest3 = "&lt;test&gt;&lt;name&gt;XYZ&lt;/name&gt;&lt;list /&gt;&lt;/test&gt;"; final Test test3 = (Test) xstream.fromXML(xmlTest3); //@formatter:off /* name: XYZ */ //@formatter:on test3.print(); // Deserialize without list-tag final String xmlTest4 = "&lt;test&gt;&lt;name&gt;XYZ&lt;/name&gt;&lt;/test&gt;"; final Test test4 = (Test) xstream.fromXML(xmlTest4); //@formatter:off /* name: XYZ * Exception in thead ... NullPointerException */ //@formatter:on test4.print(); } </code></pre> <p>we see a NullPointerException, because <code>list</code> was not initialized.</p> <p>I'd like to have the <code>list</code>-element in the XML optional similiar to test4. What can I do? Because there are many classes in my datamodel similiar to <code>Test</code>, I don't want to write a <code>Converter</code> for every class. But suppose I would write a <code>Converter</code>, how can I set the final attribute <code>name</code>?</p>
 

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