Overriding equals and hashcode for a POJO

This is an interesting case of programming where you need to compare two POJO objects. You might need to compare standalone objects or you may need to uniquely identify them in a collection. This can be achieved by overriding equals() and hashCode() methods.

Debugging a java.lang.NoClassDefFoundError

java.lang.NoClassDefFoundError is one of the most common problem while developing Java Enterprise applications. Sometimes debugging a NoClassDefFoundError can be very tedious as you might have to look for missing class dependencies in jar files and may even have to decompile sometimes.

A NoClassDefFoundError is thrown if the Java Virtual Machine or a ClassLoader instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression) and no definition of the class could be found. The searched-for class definition existed when the currently executing class was compiled, but the definition can no longer be found. In simple words, the class was available at compile time but missing during runtime.

Generating java files from XSD using Ant and JAXB

Java Architecture for XML Binding (JAXB) provides a fast and convenient way to bind XML schemas and Java representations, making it easy for Java developers to incorporate XML data and processing functions in Java applications. As part of this process, JAXB provides methods for unmarshalling (reading) XML instance documents into Java content trees, and then marshalling (writing) Java content trees back into XML instance documents. JAXB also provides a way to generate XML schema from Java objects and vice-versa.

Here we are going to talk about generating java objects from your XSD (XML Schema Definition).

Note : If you are using Maven for build, then refer this article

Excel file with Charts in Java using Apache POI

Apache POI is a powerful Java library to work with different Microsoft Office file formats such as Excel, Power point, Visio, MS Word etc. The Apache POI Project's mission is to create and maintain Java APIs for manipulating various file formats based upon the Office Open XML standards (OOXML) and Microsoft's OLE 2 Compound Document format (OLE2). In short, you can read and write MS Excel files using Java. In addition, you can read and write MS Word and MS PowerPoint files using Java. Apache POI is your Java Excel solution (for Excel 97-2008). We have a complete API for porting other OOXML and OLE2 formats and welcome others to participate.

POI has a limitation that we cannot generate charts in Excel using it. So, we have to use a xls template which contains the desired graph and update the row/cells which are used by the graph.