Java

Doing pagination with Apache iBatis SqlMaps is really simple and straightforward. Pagination is when a database connection is queried for a sublist of objects instead for the full list of objects. This is often the case for web application when it's not desirable to display the full contents of a database table to the users all at once. Hence the name pagination: the user can "scroll" through the results using pages. Each page contains a collection of objects and the pages usually are ordered.

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For analysis of memory leaks in Java applications, the heap dump is an essential source of information which is quite helpful. The dump files can be analyzed with tools like Eclipse Memory Analyzer Tool.

To get a heap dump, there are multiple ways. The first, which should be enabled in all circumstances and especially on production systems, is by adding a VM option. By enabling -XX:+HeapDumpOnOutOfMemory, a heap dump is automatically written to disk when OutOfMemoryErrors occur.

The second way is to manually force a heap dump at runtime at any point of time, without the need of an actual OutOfMemoryError. For this to work, you need to enable Java Management Extensions. Enable JMX by adding the following system properties to your launch configuration of Tomcat:


-Dcom.sun.management.jmxremote
-Dcom.sun.management.jmxremote.port="9004"
-Dcom.sun.management.jmxremote.authenticate="false"
-Dcom.sun.management.jmxremote.ssl="false"


Now run the following code to get a dump of the heap at runtime:

String url = "service:jmx:rmi:///jndi/rmi://localhost:9004/jmxrmi";
JMXServiceURL jmxURL = new JMXServiceURL(url);
JMXConnector connector = JMXConnectorFactory.connect(jmxURL);
MBeanServerConnection connection = connector.getMBeanServerConnection();
String hotSpotDiagName = "com.sun.management:type=HotSpotDiagnostic";
ObjectName name = new ObjectName(hotSpotDiagName);
String operationName = "dumpHeap";
File tempFile = File.createTempFile("heapdump", ".hprof");
tempFile.delete();
String dumpFilename = tempFile.getAbsolutePath();
Object[] params = new Object[] { dumpFilename, Boolean.TRUE };
String[] signature = new String[] { String.class.getName(), boolean.class.getName() };
Object result = connection.invoke(name, operationName, params, signature);
System.out.println("Dumped to " + dumpFilename);

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