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POHow to create recursive object graphs with Guice?
 

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  1. POHow to create recursive object graphs with Guice?
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    <p>Suppose I have 5 classes A, B, C, D, E that all implement a common interface X. Each of the classes B, C, D and E has a field of type X (so they can be seen as wrapper classes).</p> <p>Which instances are created is determined at runtime, so I could have for example one of the following object graphs:</p> <pre><code>E -&gt; D -&gt; C -&gt; B -&gt; A D -&gt; B -&gt; A E -&gt; A A </code></pre> <p>(The order is fixed and the innermost instance is always of type A, but otherwise there are no restrictions.)</p> <p>No I'd like to create this objects with Guice to avoid providing all their other dependencies by hand.</p> <p>What's the easiest way to do this? Currently it seems that I have to</p> <ol> <li>let Guice create instance of A</li> <li>create a module that binds X.class to this instance and a child injector with this additional module</li> <li>let Guice create the next instance (e.g., of type B)</li> <li>repeat 2., now binding X.class to the instance of B</li> <li>repeat 3. and 4. until all objects are created</li> </ol> <p>Is there an easier way? Could I perhaps somehow automatically register a new instance of a subclass of X as a binding for X each time it is created?</p> <p><strong>Edit: Clarification of "<em>Which instances are created is determined at runtime</em>":</strong></p> <p>My current code looks like this:</p> <pre><code>X createX() { X x = new A(dependencies); if (useB) x = new B(x, some, dependencies); if (useC) x = new C(x, further, dependencies); if (useD) x = new D(x, dependency); if (useE) x = new E(x, yet, other, dependencies); return x; } </code></pre> <p>The value of the flags useB, useC, useD, and useE comes from a properties file.</p> <p>My main goal is to save providing all the dependencies to the constructors manually.</p> <p><strong>Edit: Solution:</strong></p> <p>I have added my own solution which I have found in the meantime. Thanks to all answerers!</p> <p>A way to improve my solution would be to make it possible to remove the <code>@InInstance</code> annotation on the constructor parameters. I have experimented with type listeners, but I haven't found a way to do this. Hints would be welcome.</p>
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