In Eclipse IDE, run a Java web application with Tomcat server plugin, but the console prompts

Exception in thread "x" 
	java.lang.OutOfMemoryError: Java heap space

1. Solution – Increase Heap Size in Tomcat

By default, Tomcat allocated a small amount of heap size. To solve it, you need to increase the Tomcat’s heap size manually.

1.1 In server view, double clicks on the Tomcat Server icon.

1.2 Clicks on the “Open launch configuration” link.

1.3 Clicks on the “Arguments” tab, and append the following VM options at the end of the VM arguments :

-Xms<size> - Set initial Java heap size
-Xmx<size> - Set maximum Java heap size

In this example, we increase the heap size to -Xms512m -Xmx1024m, it should be enough for most of the projects.

2. Know Your Heap Size

To know how much heap size is allocated in Tomcat, append this VM option -XX:+PrintFlagsFinal (refer figure 1.3). Start Tomcat, you will noticed the entire VM values are dump to the console, find following names :

1. InitialHeapSize
2. MaxHeapSize

P.S The value is in bytes.

References

1. Java heap memory size