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POJackson deserializing with custom deserializer causes a lot of GC calls and takes a lot longer
 

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  1. POJackson deserializing with custom deserializer causes a lot of GC calls and takes a lot longer
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    <p>To solve my type mismatch problem discussed <a href="https://stackoverflow.com/questions/12684808/jackson-parser-ignore-deserializing-for-type-mismatch/">in this thread</a> I created custom <code>Deserializers</code> and added them to <code>ObjectMapper</code>. However the performance deteriorates significantly with this.</p> <p>With default deserializer i get 1-2 Garbage collection calls in <code>logcat</code> while with custom deserializer there are at least 7-8 GC calls, and hence the processing time is also increase significantly.</p> <p>My Deserializer :</p> <pre><code>public class Deserializer&lt;T&gt; { public JsonDeserializer&lt;T&gt; getDeserializer(final Class&lt;T&gt; cls) { return new JsonDeserializer&lt;T&gt; (){ @Override public T deserialize(JsonParser jp, DeserializationContext arg1) throws IOException, JsonProcessingException { JsonNode node = jp.readValueAsTree(); if (node.isObject()) { return new ObjectMapper().convertValue(node, cls); } return null; } }; } } </code></pre> <p>And I am using this to add to Mapper</p> <pre><code>public class DeserializerAttachedMapper&lt;T&gt; { public ObjectMapper getMapperAttachedWith(final Class&lt;T&gt; cls , JsonDeserializer&lt;T&gt; deserializer) { ObjectMapper mapper = new ObjectMapper(); SimpleModule module = new SimpleModule(deserializer.toString(), new Version(1, 0, 0, null, null, null)); module.addDeserializer(cls, deserializer); mapper.registerModule(module); return mapper; } } </code></pre> <p><strong>EDIT:</strong> Added extra data</p> <p>My JSON is of considerable size but not huge: I have pasted <a href="http://pastie.org/5170282" rel="nofollow noreferrer">it here</a></p> <p>Now for parsing the same JSON if i use this code:</p> <pre><code> String response = ConnectionManager.doGet(mAuthType, url, authToken); FLog.d("location object response" + response); // SimpleModule module = new SimpleModule("UserModule", new Version(1, 0, 0, null, null, null)); // JsonDeserializer&lt;User&gt; userDeserializer = new Deserializer&lt;User&gt;().getDeserializer(User.class); // module.addDeserializer(User.class, userDeserializer); ObjectMapper mapper = new ObjectMapper(); // mapper.registerModule(module); JsonNode tree = mapper.readTree(response); Integer code = Integer.parseInt(tree.get("code").asText().trim()); if(Constants.API_RESPONSE_SUCCESS_CODE == code) { ExploreLocationObject locationObject = mapper.convertValue(tree.path("response").get("locationObject"), ExploreLocationObject.class); FLog.d("locationObject" + locationObject); FLog.d("locationObject events" + locationObject.getEvents().size()); return locationObject; } return null; </code></pre> <p>Then my logcat is <a href="http://pastie.org/5170336" rel="nofollow noreferrer">like this</a></p> <p>But if I use this code for same JSON</p> <pre><code> String response = ConnectionManager.doGet(mAuthType, url, authToken); FLog.d("location object response" + response); SimpleModule module = new SimpleModule("UserModule", new Version(1, 0, 0, null, null, null)); JsonDeserializer&lt;User&gt; userDeserializer = new Deserializer&lt;User&gt;().getDeserializer(User.class); module.addDeserializer(User.class, userDeserializer); ObjectMapper mapper = new ObjectMapper(); mapper.registerModule(module); JsonNode tree = mapper.readTree(response); Integer code = Integer.parseInt(tree.get("code").asText().trim()); if(Constants.API_RESPONSE_SUCCESS_CODE == code) { ExploreLocationObject locationObject = mapper.convertValue(tree.path("response").get("locationObject"), ExploreLocationObject.class); FLog.d("locationObject" + locationObject); FLog.d("locationObject events" + locationObject.getEvents().size()); return locationObject; } return null; </code></pre> <p>Then my logcat is <a href="http://pastie.org/5170352" rel="nofollow noreferrer">like this</a></p>
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    1. COOne additional comment: make absolutely sure you reuse `ObjectMapper` -- it is a heavy-weight object and should not be created once per request. Otherwise it could definitely cause lots of GC activity. Hard to know for sure from just code above.
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    2. COActually I noticed that your deserializer creates an ObjectMapper: this is very costly. You can avoid that by using `JsonParser.getCodec()`, casting result to `ObjectMapper` (which is safe upcast). That should help quite a bit too.
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      1. USStaxMan
    3. COI modified my code and added object mapper to my singleton, the performance improved for default deserializer but the problem with custom deserializer is still there. Also, I noticed that if i add two deserializers to same module then the default deserializer gets called not the custom one. The `JsonParser.getCodec()` isn't a static method , so I will have to create `JsonParser` for each request. won't that be expensive too??
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