jaxb
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jaxb [2012/08/26 17:16] hkoller [Using JAXB with Maven] |
jaxb [2012/08/26 17:23] (current) hkoller [Using JAXB with Maven] |
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| + | The **Java Architecture for XML Binding** (JAXB) allows Java developers to map Java classes to XML representations. JAXB provides two main features: the ability to marshal Java objects into XML and the inverse, i.e. to unmarshal XML back into Java objects. | ||
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| + | ====== JAXB with Maven ====== | ||
| + | JAXB can be combined with Maven using the [[http://java.net/projects/maven-jaxb2-plugin/pages/Home | maven-jaxb2-plugin ]]. The Maven build can then use the JAXB binding compiler (**xjc**) to generate a package of Java classes from an XML schema. | ||
| + | ===== Configuring pom.xml ===== | ||
| + | ** Add dependency to jaxb-api ** | ||
| + | <code xml> | ||
| + | <dependency> | ||
| + | <groupId>javax.xml</groupId> | ||
| + | <artifactId>jaxb-api</artifactId> | ||
| + | <version>2.1</version> | ||
| + | </dependency> | ||
| + | </code> | ||
| + | |||
| + | ** Create classes from XSD file during build ** | ||
| + | <code xml> | ||
| + | <build> | ||
| + | <plugins> | ||
| + | <plugin> | ||
| + | <groupId>org.jvnet.jaxb2.maven2</groupId> | ||
| + | <artifactId>maven-jaxb2-plugin</artifactId> | ||
| + | <executions> | ||
| + | <execution> | ||
| + | <goals> | ||
| + | <goal>generate</goal> | ||
| + | </goals> | ||
| + | </execution> | ||
| + | </executions> | ||
| + | </plugin> | ||
| + | </plugins> | ||
| + | </build> | ||
| + | </code> | ||
| + | |||
| + | xjc per default searches for XSD files in the directory //src/main/resources// and generates the classes to //target/generated-sources/xjc/// | ||
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| + | |||
| + | ====== Marshalling ====== | ||
| + | |||
| + | <code java> | ||
| + | |||
| + | // create a request object | ||
| + | Request request = new Request(); // Request is defined in the XML Schema, classes generated with xjc | ||
| + | request.setId(123); // set more parameters if required | ||
| + | |||
| + | // create XML | ||
| + | ByteArrayOutputStream requestXML = new ByteArrayOutputStream(); | ||
| + | JAXB.marshal(request, requestXML); | ||
| + | System.out.println(requestXML); | ||
| + | |||
| + | </code> | ||
| + | |||
| + | |||
| + | ====== Unmarshaling ====== | ||
| + | Assume you have an XML File which contains a Result object. (and the corresponding java classes have been generated from an XML Schema using xjc) | ||
| + | |||
| + | <code java> | ||
| + | StreamSource s = new StreamSource(new FileInputStream("file.xml")); | ||
| + | |||
| + | JAXBContext jaxbContext = JAXBContext.newInstance("my.name.space"); | ||
| + | Unmarshaller u = jaxbContext.createUnmarshaller(); | ||
| + | Result r = u.unmarshal(s, Result.class).getValue(); | ||
| + | |||
| + | </code> | ||
| + | |||
| + | **Note:** | ||
| + | For some reason xjc does not always generate the correct **@RootElement** annotations in the class definitions. As a result the unmarshaller might complain about a missing namespace when we try to unmarshal like this: | ||
| + | |||
| + | <code java> | ||
| + | Result r = (Result) u.unmarshal(s) | ||
| + | </code> | ||
| + | |||
| + | To fix this we need to explicitly tell the unmarshaller which class it should unmarshal by passing it the **//Result.class//** as parameter. For details see: | ||
| + | * http://weblogs.java.net/blog/kohsuke/archive/2006/03/why_does_jaxb_p.html | ||
| + | * http://stackoverflow.com/questions/819720/no-xmlrootelement-generated-by-jaxb | ||
| + | * http://magicmonster.com/kb/prg/java/ws/jaxb/expected_elements_are_none_xjc_fix.html | ||
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