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JBoss Reflect Performance Javassist vs Introspection
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reply from <a href="http://community.jboss.org/people/kabir.khan%40jboss.com">Kabir Khan</a> in <i>JBoss Microcontainer Development</i> - <a href="http://community.jboss.org/message/537476#537476">View the full discussion</a>
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<div class="jive-rendered-content"><p>What we generate is effectively something along the lines of</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code jive-java"><font color="navy"><b>public</b></font> <font color="navy"><b>class</b></font> JavassistMethod1 <font color="navy"><b>implements</b></font> JavassistMethod
<font color="navy">{</font>
   <font color="navy"><b>public</b></font> Object invoke(Object target, Object[] args) <font color="navy"><b>throws</b></font> Throwable
   <font color="navy">{</font>
      <font color="navy"><b>if</b></font> (target == <font color="navy"><b>null</b></font>)
         <font color="navy"><b>throw</b></font> <font color="navy"><b>new</b></font> IllegalArgumentException(<font color="red">"Null target"</font>);
      <font color="navy"><b>if</b></font> (target <font color="navy"><b>instanceof</b></font> SomeClass == <font color="navy"><b>false</b></font>)
         <font color="navy"><b>throw</b></font> <font color="navy"><b>new</b></font> IllegalArgumentException(<font color="red">"Wrong target"</font>);
     
      <font color="navy"><b>if</b></font> (args == <font color="navy"><b>null</b></font> || args.length != 10)
         <font color="navy"><b>throw</b></font> <font color="navy"><b>new</b></font> IllegalArgumentException(<font color="red">"Wrong number of parameters"</font>);
     
      <font color="navy"><b>if</b></font> (args[0] == <font color="navy"><b>null</b></font>)
         <font color="navy"><b>throw</b></font> <font color="navy"><b>new</b></font> IllegalArgumentException(<font color="red">"Parameter 1 cannot be null for SomeClass.someMethod(long, String)"</font>);
      <font color="navy"><b>if</b></font> (args[0] != <font color="navy"><b>null</b></font> && args[0] <font color="navy"><b>instanceof</b></font> Long == <font color="navy"><b>false</b></font>)
         <font color="navy"><b>throw</b></font> <font color="navy"><b>new</b></font> IllegalArgumentException(<font color="red">"Parameter 1 is not an instance of Long for SomeClass.someMethod(long, String)"</font>);
     
      <font color="navy"><b>if</b></font> (args[1] != <font color="navy"><b>null</b></font> && args[1] <font color="navy"><b>instanceof</b></font> String == <font color="navy"><b>false</b></font>)
         <font color="navy"><b>throw</b></font> <font color="navy"><b>new</b></font> IllegalArgumentException(<font color="red">"Parameter 2 is not an instance of String for SomeClass.someMethod(long, String)"</font>);
     
      <font color="navy"><b>return</b></font> ((SomeClass)target).someMethod(((Long)args[0]).longValue(), (String)args[1]);     
   <font color="navy">}</font>
<font color="navy">}</font>
</code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Disabling the parameter checking so we end up with this instead reduces the time spent in C from about 4.8s to 3.8s</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code jive-java"><font color="navy"><b>public</b></font> <font color="navy"><b>class</b></font> JavassistMethod1 <font color="navy"><b>implements</b></font> JavassistMethod
<font color="navy">{</font>
   <font color="navy"><b>public</b></font> Object invoke(Object target, Object[] args) <font color="navy"><b>throws</b></font> Throwable
   <font color="navy">{</font>
      <font color="navy"><b>return</b></font> ((SomeClass)target).someMethod(((Long)args[0]).longValue(), (String)args[1]);     
 
   <font color="navy">}</font>
<font color="navy">}</font>
 
</code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Profiling this, for each JavassistMethod implementation the time taken is roughly</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>50% generating the bytecode for the method </p><p>30% Converting the bytecode to a byte array and creating the class</p><p>13% creating the constructor</p><p>6% setting the interfaces</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Maybe a better approach would be</p><p>1) to do the parameter checking in Javassist[Constructor/Method/Field]Info itself</p><p>2) to generate less classes? Something like:</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code jive-java"><font color="navy"><b>public</b></font> <font color="navy"><b>class</b></font> SomeBeanAccessor <font color="navy"><b>implements</b></font> JavassistBeanAccessor
<font color="navy">{</font>
    <font color="navy"><b>public</b></font> Object newInstance(<font color="navy"><b>int</b></font> index, Object[] args) <font color="navy"><b>throws</b></font> Throwable
    <font color="navy">{</font>
       <font color="navy"><b>if</b></font> (index == 0)
          <font color="navy"><b>return</b></font> <font color="navy"><b>new</b></font> SomeClass((String)args[0]);
       <font color="navy"><b>else</b></font> <font color="navy"><b>if</b></font> (index == 1)
          <font color="navy"><b>return</b></font> <font color="navy"><b>new</b></font> SomeClass((String)args[1]);
 
       <font color="navy"><b>return</b></font> <font color="navy"><b>null</b></font>;
    <font color="navy">}</font>
 
    <font color="navy"><b>public</b></font> Object invoke(<font color="navy"><b>long</b></font> hash, Object target, Object[] args) <font color="navy"><b>throws</b></font> Throwable
    <font color="navy">{</font>
        <font color="navy"><b>if</b></font> (hash == 121267912)
      <font color="navy"><b>return</b></font> ((SomeClass)target).someMethod(((Long)args[0]).longValue(), (String)args[1]);
    <font color="navy"><b>if</b></font> (hash == 128172981)
 
      <font color="navy"><b>return</b></font> ((SomeClass)target).otherMethod(((Long)args[0]).longValue(), (String)args[1], (String)args[2]);
 
   <font color="navy">}</font>
 
 
 
   <font color="navy"><b>public</b></font> Object get(String name, Object target) <font color="navy"><b>throws</b></font> Throwable
 
   <font color="navy">{</font>
 
      <font color="navy"><b>if</b></font> (name.equals(<font color="red">"intField"</font>)
 
          <font color="navy"><b>return</b></font> Integer.valueOf(((SomeClass)target).intField);
 
      <font color="navy"><b>if</b></font> (name.equals(<font color="red">"stringField"</font>)
 
          <font color="navy"><b>return</b></font> ((SomeClass)target).stringField;
 
   <font color="navy">}</font>
 
 
 
   <font color="navy"><b>public</b></font> <font color="navy"><b>void</b></font> set(String name, Object target, Object value) <font color="navy"><b>throws</b></font> Throwable
 
   <font color="navy">{</font>
 
      <font color="navy"><b>if</b></font> (name.equals(<font color="red">"intField"</font>)
 
          ((SomeClass)target).intField = ((Integer)value).intValue();
 
          <font color="navy"><b>return</b></font>;
 
      <font color="navy"><b>if</b></font> (name.equals(<font color="red">"stringField"</font>)
 
          ((SomeClass)target).stringField = (String)value;
 
   <font color="navy">}</font>
 
<font color="navy">}</font>
 
</code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>First call by Javassist[Constructor/Method/Field]Info to access the member would result in this being created for ALL members, and cached in JavassistTypeInfo. </p></div>
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