Wednesday, April 16, 2014

Maven Compile error

Maven Compile Plugin by default uses version 2.0.2 and JDK1.3 as the target for the compilation of Java code if you do not specify the compiler plugin version and the Java source & target versions. Due to this, you may get the below error when compiling:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.0.2:compile (default-compile) on project scratch: Compilation failure
[ERROR] /home/projects/java/scratch/src/main/java/com/test/[50,26] error: for-each loops are not supported in -source 1.3

To resolve this problem, you need to specify the compiler plugin version and the Java -source and -target versions in the pom.xml of your project as below:


You can figure out the latest version of the Compiler Plugin by reading the version number on the top right of the Compiler Plugin page.

Saturday, April 12, 2014

Throttle task submission in Java - Simple solution

JDK provides a convenient java.util.concurrent.Executors factory with useful methods to return various java.util.concurrent.Executor implementation instance pre-configured with commonly used settings. However, there is no implementation or configuration available for an implementation that throttles task submission. Here I provide my take on a very simple solution for this requirement.

private void submitTasks(List tasksList) {
  final ThreadPoolExecutor executor = new ThreadPoolExecutor(MIN_POOL_SIZE,
                                                             new LinkedBlockingQueue());
  for (Runnable task : tasksList) {
    while (executor.getQueue().size() > MAX_Q_SIZE) {
      // Throttle for WAIT_FOR_SECONDS seconds if queue is full
      try {"Waiting " + WAIT_FOR_SECONDS + " seconds as Queue size is: " + executor.getQueue().size());
        Thread.sleep(WAIT_FOR_SECONDS * 1000);
      } catch (InterruptedException e) {
        // Ignore
  // inform the executor there are no more tasks

Instead of using the factory to get a pre-configured executor, I create my own ThreadPoolExecutor using a LinkedBlockingQueue. This allows us access to the underlying queue for the throttling feature. Before submitting the task, I check if the current queue size is greater than a certain size and if so, then wait for a configured time repeatedly till the queue is smaller.
This implementation is very useful for the scenarios where you have lots of short running tasks that need to be processed by a fixed small number of threads.


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