JAXB is a set of tools and libraries used to generate class libraries specifically to parse a defined XML schema. Java classes can be generated automatically for an XML schema as defined by an XSD file or can be coded manually.
This tutorial will show an example of using JAXB to generate classes automatically from an XSD. The generated library will be used for parsing of an XML file conforming to the specified XSD schema.
Two approaches can be taken. One is to use the Java JDK with the JAXB jar library and the other is to use the Java JDK exclusivly. Apache Ant script examples for each approach are provided below.
As a prerequisite the Java JDK need to be installed. See our tutorial on installing Java on Linux. This example was compiled and run with jdk1.8.0_112
If using the JAXB jar libraries, download the latest JAXB jar libraries from: JAXB home page
cd /opt unzip ~/Downloads/jaxb-ri-2.2.11.zip
.. . # # JAXB # if [ -d /opt/jaxb-ri ] then PATH=/opt/jaxb-ri/bin:$PATH export CLASSPATH=/opt/jaxb-ri/lib/jaxb-xjc.jar:$CLASSPATH fi . ..
Simple but less desirable (jar only and not complete SDK) alternative: The JAXB jaxb-xjc.jar, is available as a JAR file and can be placed in /opt/java/latest/lib/. See: FindJar.com
If using JBoss, your CLASSPATH can reference JAXB from the JBoss library: /opt/jboss-X.X.X.XXXXX/lib/jaxb-xjc.jar
Define an XML schema file (XSD) using your favorite XSD/XML editor:
File: corporation.xsd XML Schema File: corporation.xsd
XSD requires that element attributes be defined at the end of the element definition.
Complex types allow elements in their content and may carry attributes. The «complexType» section refers to how the content (defined by elements) is formed. Simple types do not have element content and cannot carry attributes. SimpleTypes are used to define and use a new type like an enum. SimpleTypes are also used to set restrictions such as maxLength/minLength, max/min values, number of characters (length), totalDigits, etc.
Multiple occurances of an element type is permitted when the following is specified:
element attribute maxOccurs="unbounded" is specified. or maxOccurs="10" is specified as a specific value greater than one.
element attribute minOccurs="3" is specified as a value greater than one.
Generate a Java class library files from the XSD: xjc -d ./ corporation.xsd For a description of commands try: xjc -help or java -jar $JAVA_HOME/lib/jaxb-xjc.jar -help
The following ant snippet will be used to perform this task:
package com.megacorp.projectx.xml; /** * Checked exception thrown by Data Access Service layer to clients to report * system level errors. */ public class JAXBXMLException extends Exception < /** * Construct a JAXBXMLException with no arguments. */ public JAXBXMLException() < super(); >public JAXBXMLException(Exception e) < super(e); >/** * Construct a JAXBXMLException with the specified message ID. */ public JAXBXMLException( String msg ) < super( msg ); >/** * @param message * @param exception */ public JAXBXMLException(String message, Exception exception) < super(message, exception); >>
Corporation MegaX1-800-555-12121-877-555-1212 512 Megacorp Way, Gotham City Mr Grand Kahuna1None19981-800-555-12131-800-555-1214 100 Cherry Hill Lane, Gotham City Mr Special Tee123-45-67881-817-555-1212ABC Consulting3 Mockingbird Lane, Smallville AKCorpToIndividual1-800-555-12151-800-555-1216 200 Lookout Hill, Gotham City Mrs Jenny Reliable2Mr Grand Kahuna19991-800-555-12171-800-555-1218 300 Riverside View, Gotham City
1) Use the JAXB jar with the «xjc» directive:
Ant build script: build.xml
[user1@tux JavaJaxb]$ ant compile ant compileBuildfile: /home/user1/Desktop/JavaJaxb/build.xml jaxb: [echo] Compiling the schema. [mkdir] Created dir: /home/user1/Desktop/JavaJaxb/gen-src/com/megacorp/projectx/xml/jaxb [xjc] Compiling file:/home/user1/Desktop/JavaJaxb/corporation.xsd [xjc] Writing output to /home/user1/Desktop/JavaJaxb/gen-src compile: [echo] Compiling the java source files. [javac] Compiling 9 source files to /home/user1/Desktop/JavaJaxb/classes [javac] Note: /home/user1/Desktop/JavaJaxb/src/com/megacorp/projectx/xml/JAXBXMLHandler.java uses unchecked or unsafe operations. [javac] Note: Recompile with -Xlint:unchecked for details. BUILD SUCCESSFUL Total time: 1 second
[Potential Pitfall]: You may get the following error: taskdef class com.sun.tools.xjc.XJCTask cannot be found This typically means that jaxb-xjc.jar is missing from your classpath
[user1@tux JavaJaxb]$ ant run run: [echo] Running the sample application. [java] Corporation: Corporation MegaX [java] Corp address: 512 Megacorp Way, Gotham City [java] There are 3 employees. [java] Employees: [java] Employee Name: Mr Grand Kahuna [java] Tax Status: US-W2 [java] Gender: Male [java] Work Phone: 1-800-555-1213 [java] Employee Number: 1 [java] Manager: None [java] Start Year: 1998 [java] Employee Name: Mr Special Tee [java] Tax Status: US-1099 [java] Gender: Male [java] Work Phone: 1-800-555-1215 [java] SSN Number: 123-45-6788 [java] Corp Name: ABC Consulting [java] Hire Relationship: CorpToIndividual [java] Employee Name: Mrs Jenny Reliable [java] Tax Status: US-W2 [java] Gender: Female [java] Work Phone: 1-800-555-1217 [java] Employee Number: 2 [java] Manager: Mr Grand Kahuna [java] Start Year: 1999
2) Reference the Java JDK only:
This method does not require the JAXB jar file and relies on JAXB as it resides in the JDK. The only change in the Ant build script is the target «jaxb» which will execute the Java «xjc» compiler to generate the parser code.
Ant build script: build.xml
Note that the JAXB execution requires the «xjc» command to be in your path. This is typically /opt/java/latest/bin/
Unlike Ant which explicitly specifies the configuration, Maven requires that the user operate under its convention. Maven expects to find source located in directories specified by its convention. Thus use the following directory layout:
Corporation: Corporation MegaX Corp address: 512 Megacorp Way, Gotham City There are 3 employees. Employees: Employee Name: Mr Grand Kahuna Tax Status: US-W2 Gender: Male Work Phone: 1-800-555-1213 Employee Number: 1 Manager: None Start Year: 1998 Employee Name: Mr Special Tee Tax Status: US-1099 Gender: Male Work Phone: 1-800-555-1215 SSN Number: 123-45-6788 Corp Name: ABC Consulting Hire Relationship: CorpToIndividual Employee Name: Mrs Jenny Reliable Tax Status: US-W2 Gender: Female Work Phone: 1-800-555-1217 Employee Number: 2 Manager: Mr Grand Kahuna Start Year: 1999
Our example above is for a standard XML file containing only XML content. This is common for configuration files. This is specified in our example by the XML XSD schema:
One can also have mixed content where there is plain text around the XML content. The XSD would be stated as:
and the XML would have plain text mixed with the XML as in this example snippet:
JAXB can handle a complexType with a «mixed» text of both «true» and «false» but only with a substantial change to the code. First note the the generated code is different: