How to obtain the errors from a Pentaho job using the Java API?

I'm executing some Pentaho jobs using the following code (not mine, just from a legacy app. I must change the code if needed):

JobMeta jobMeta = new JobMeta(jobName, null);
Job job = new Job(null, jobMeta);
job.start();
job.waitUntilFinished();

if (job.getErrors() != 0) {
    logger.error("Error encountered!");
    throw new RuntimeException(getTrace(job.getStackTrace()));
}

//...

private String getTrace(StackTraceElement[] elements) {
    StringBuilder sb = new StringBuilder();
    for (StackTraceElement element : elements) {
        sb.append(element.toString());
    }
    return sb.toString();
}

Everything seems to be fine but the if statement returns true and I get a crappy non-sensical message like this:

2015-03-29 16:30:43,658 INFO  [com.foo.bar.component.ETLComponent] ERROR on job /home/path/to/pentaho/jobs/main_job.kjb
java.lang.RuntimeException:
        at com.foo.barpentaho.KettleService.executeJob(KettleService.java:48)  //my class
        at com.foo.bar.component.ETLComponent.process(ETLComponent.java:64)    //my class
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.mule.model.resolvers.AbstractEntryPointResolver.invokeMethod(AbstractEntryPointResolver.java:151)
        at org.mule.model.resolvers.ExplicitMethodEntryPointResolver.invoke(ExplicitMethodEntryPointResolver.java:93)
        at org.mule.model.resolvers.DefaultEntryPointResolverSet.invoke(DefaultEntryPointResolverSet.java:39)
        at org.mule.component.DefaultComponentLifecycleAdapter.invoke(DefaultComponentLifecycleAdapter.java:350)
        at org.mule.component.AbstractJavaComponent.invokeComponentInstance(AbstractJavaComponent.java:86)
        at org.mule.component.AbstractJavaComponent.doInvoke(AbstractJavaComponent.java:77)
        at org.mule.component.AbstractComponent.invokeInternal(AbstractComponent.java:126)
        at org.mule.component.AbstractComponent.access$000(AbstractComponent.java:61)
        at org.mule.component.AbstractComponent$1$1.process(AbstractComponent.java:242)
        at org.mule.processor.chain.DefaultMessageProcessorChain.doProcess(DefaultMessageProcessorChain.java:99)
        at org.mule.processor.chain.AbstractMessageProcessorChain.process(AbstractMessageProcessorChain.java:66)
        at org.mule.processor.chain.InterceptingChainLifecycleWrapper.doProcess(InterceptingChainLifecycleWrapper.java:56)
        at org.mule.processor.chain.AbstractMessageProcessorChain.process(AbstractMessageProcessorChain.java:66)
        at org.mule.processor.chain.InterceptingChainLifecycleWrapper.process(InterceptingChainLifecycleWrapper.java:87)
        at org.mule.component.AbstractComponent.process(AbstractComponent.java:160)
        at org.mule.processor.chain.DefaultMessageProcessorChain.doProcess(DefaultMessageProcessorChain.java:99)
        at org.mule.processor.chain.AbstractMessageProcessorChain.process(AbstractMessageProcessorChain.java:66)
        at org.mule.processor.AbstractInterceptingMessageProcessorBase.processNext(AbstractInterceptingMessageProcessorBase.java:105)
        at org.mule.interceptor.AbstractEnvelopeInterceptor.process(AbstractEnvelopeInterceptor.java:55)
        at org.mule.processor.AsyncInterceptingMessageProcessor.processNextTimed(AsyncInterceptingMessageProcessor.java:111)
        at org.mule.processor.AsyncInterceptingMessageProcessor$AsyncMessageProcessorWorker.doRun(AsyncInterceptingMessageProcessor.java:158)
        at org.mule.work.AbstractMuleEventWork.run(AbstractMuleEventWork.java:43)
        at org.mule.work.WorkerContext.run(WorkerContext.java:310)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:662)

Searching on the net, I find this code from the Pentaho API examples (uses Pentaho 5 but the idea remains the same):

String filename = "..."; //path for the job to execute
TransMeta transMeta = new TransMeta(filename);
Trans trans = new Trans(transMeta);

trans.execute(null); // You can pass arguments instead of null.
trans.waitUntilFinished();
if ( trans.getErrors() > 0 )
{
  throw new RuntimeException( "There were errors during transformation execution." );
}

So I will get a non-sensical message again. I've searched into the javadoc and there's no useful info obtain the results with errors.

How can I obtain the proper error messages from the results of the Pentaho job executed?

I'm using Pentaho 4.3.

Solution

CentralLogStore can be used to get proper error messages from Job execution step. I am using following code for the same purpose in Custom Java Api:

    job.waitUntilFinished();
    if (job.getErrors() > 0) {
      Log4jBufferAppender appender = CentralLogStore.getAppender();
      appender.removeGeneralMessages();
      String logText = appender.getBuffer(job.getLogChannelId(), false).toString();
      CentralLogStore.discardLines(job.getLogChannelId(), false);
      throw new RuntimeException(logText);
    }

And the error messages look like:

Job-62001 Error in [Processes/SubProcesses/ETL Report Transformation Process.process/Get Record Count]
Running Get_Number_Of_Records Transformation occurred error.
caused by: org.pentaho.di.core.exception.KettleException: 
We failed to initialize at least one step.  Execution can not begin!
    at org.pentaho.di.trans.Trans.prepareExecution(Trans.java:823)
    ...

More details can be found on the wiki here.