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In this post I will show how to build CRUD (Create, Read, Update, Delete) REST-ful (Representational State Transfer) services using Spring Framework. Spring Framework version used in this example is 3.0.6.RELEASE. Apache Tomcat version used for testing the web services is 6.0.29 (default Tomcat version used by Tomcat Maven Plugin of Apache Maven 2.2.1). Project sources are available for download. So let’s start, step by step: First we have to define the resource on which the CRUD operation will be performed and how this resource will be represented. In our example we will use a resource that represents a User. The resource will be represented using XML (Extensible Markup Language). At the end of the post I will show how you can switch the resource representation to JSON (JavaScript Object Notation) or any other supported form. Create a Maven project. We will use Maven for project management and build. Maven POM is shown below: <?xml version="1.0"?> <project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <modelVersion>4.0.0</modelVersion> <groupId>org.zmeu</groupId> <artifactId>zmeu-blog-spring-rest</artifactId> <version>1.0.0-SNAPSHOT</version> <packaging>war</packaging> <name>ZMEU Blog Spring REST</name> <build> <pluginManagement> <plugins> <plugin> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>1.6</source> <target>1.6</target> </configuration> </plugin> </plugins> </pluginManagement> </build> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-web</artifactId> <version>3.0.6.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>3.0.6.RELEASE</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-lang3</artifactId> <version>3.0</version> </dependency> <!-- Logging dependencies --> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> <version>1.6.1</version> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> <version>1.6.1</version> <scope>runtime</scope> </dependency> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.16</version> <scope>runtime</scope> </dependency> <!-- Testing dependencies --> <dependency> <groupId>org.testng</groupId> <artifactId>testng</artifactId> <version>6.2</version> <scope>test</scope> </dependency> </dependencies> </project> Write User class that will represent our resource. Due to fact that we have decided to represent our resource using XML, we will annotate our class using JAXB (Java Architecture for XML Binding) annotations. When JAXB is used, Spring requires java classes to be annotated with @XmlRootElement (see Jaxb2RootElementHttpMessageConverter). If you are using Java 6 then you don’t have to do anything special because Java 6 is coming already with JAXB2, otherwise you will have to include dependencies to JAXB into your project. You can see below the User.java listing: package org.zmeu.blog.spring.rest.domain; import java.util.Date; import javax.xml.bind.annotation.XmlAccessType; import javax.xml.bind.annotation.XmlAccessorType; import javax.xml.bind.annotation.XmlRootElement; import javax.xml.bind.annotation.XmlType; import org.apache.commons.lang3.builder.EqualsBuilder; import org.apache.commons.lang3.builder.HashCodeBuilder; import org.apache.commons.lang3.builder.ToStringBuilder; @XmlAccessorType(XmlAccessType.PROPERTY) @XmlType(name = "userType") @XmlRootElement(name = "user") public class User { private long id; private String name; private Date registrationDate; public long getId() { return id; } public void setId(long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Date getRegistrationDate() { return registrationDate; } public void setRegistrationDate(Date registrationDate) { this.registrationDate = registrationDate; } @Override public String toString() { ToStringBuilder builder = new ToStringBuilder(this); builder.append("id", getId()); builder.append("name", getName()); builder.append("registrationDate", getRegistrationDate()); return builder.toString(); } @Override public boolean equals(Object obj) { if (this == obj) { return true; } if (obj == null) { return false; } if (!(obj instanceof User)) { return false; } User other = (User) obj; EqualsBuilder equalsBuilder = new EqualsBuilder(); equalsBuilder.append(getId(), other.getId()); return equalsBuilder.isEquals(); } @Override public int hashCode() { HashCodeBuilder hashCodeBuilder = new HashCodeBuilder(); hashCodeBuilder.append(getId()); return hashCodeBuilder.toHashCode(); } } In order to represent a list of users we will create a new class UserList.java package org.zmeu.blog.spring.rest.domain; import java.util.ArrayList; import java.util.List; import javax.xml.bind.annotation.XmlAccessType; import javax.xml.bind.annotation.XmlAccessorType; import javax.xml.bind.annotation.XmlElement; import javax.xml.bind.annotation.XmlRootElement; import javax.xml.bind.annotation.XmlType; @XmlAccessorType(XmlAccessType.PROPERTY) @XmlType(name = "userListType") @XmlRootElement(name = "userList") public class UserList { private List<User> users = new ArrayList<User>(); public UserList() {} public UserList(List<User> users) { this.users = users; } @XmlElement(name = "user") public List<User> getUsers() { return users; } public void setUsers(List<User> users) { this.users = users; } } Write a Spring service that will provide CRUD operations for our resource. In our case this is a simple service which uses a java.util.Map for storage. Normally this should be a service that performs some validations and delegates the persistence activities to a DAO (Data Access Object). First define the interface UserService.java: package org.zmeu.blog.spring.rest.service; import java.util.Collection; import org.zmeu.blog.spring.rest.domain.User; public interface UserService { User create(User user); User read(long userId); User update(User user); User delete(long userId); Collection<User> list(); } And after the implementation UserServiceImpl.java: package org.zmeu.blog.spring.rest.service; import java.util.Collection; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ConcurrentMap; import java.util.concurrent.atomic.AtomicLong; import org.apache.commons.lang3.Validate; import org.springframework.stereotype.Service; import org.zmeu.blog.spring.rest.domain.User; @Service public class UserServiceImpl implements UserService { private final AtomicLong USER_ID_SEQ = new AtomicLong(); private final ConcurrentMap<Long, User> usersMap = new ConcurrentHashMap<Long, User>(); @Override public User create(User user) { user.setId(USER_ID_SEQ.incrementAndGet()); usersMap.put(user.getId(), user); return user; } @Override public User read(long userId) { return usersMap.get(userId); } @Override public User update(User user) { User updatedUser = usersMap.replace(user.getId(), user); Validate.isTrue(updatedUser != null, "Unable to find user with id: " + user.getId()); return updatedUser; } @Override public User delete(long userId) { User removedUser = usersMap.remove(userId); Validate.isTrue(removedUser != null, "Unable to find user with id: " + userId); return removedUser; } @Override public Collection<User> list() { return usersMap.values(); } } Write a Spring MVC controller that will do the actual work required by a RESTful service. Our controller maps to the following locations: URL HTTP Method Description http://host:port/servletContextPath/users GET Retrieves the user list. http://host:port/servletContextPath/users POST Creates a new user. http://host:port/servletContextPath/users/12 GET Retrieves user with id = 12. http://host:port/servletContextPath/users/12 PUT Updates user with id = 12. http://host:port/servletContextPath/users/12 DELETE Deletes user with id = 12. Below you can see UserController.java source code: package org.zmeu.blog.spring.rest.controller; import java.util.ArrayList; import org.apache.commons.lang3.Validate; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.http.HttpStatus; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.ExceptionHandler; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RequestBody; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestMethod; import org.springframework.web.bind.annotation.ResponseBody; import org.springframework.web.bind.annotation.ResponseStatus; import org.zmeu.blog.spring.rest.domain.User; import org.zmeu.blog.spring.rest.domain.UserList; import org.zmeu.blog.spring.rest.service.UserService; @Controller @RequestMapping(value = "/users") public class UserController { private static final Logger LOGGER = LoggerFactory.getLogger(UserController.class); @Autowired private UserService userService; @RequestMapping(method = RequestMethod.POST) @ResponseBody public User create(@RequestBody User user) { LOGGER.info("Creating new user {}", user); return userService.create(user); } @RequestMapping(value = "/{userId}", method = RequestMethod.GET) @ResponseBody public User read(@PathVariable(value = "userId") long userId) { LOGGER.info("Reading user with id {}", userId); User user = userService.read(userId); Validate.isTrue(user != null, "Unable to find user with id: " + userId); return user; } @RequestMapping(value = "/{userId}", method = RequestMethod.PUT) @ResponseStatus(value = HttpStatus.NO_CONTENT) public void update(@PathVariable(value = "userId") long userId, @RequestBody User user) { LOGGER.info("Updating user with id {} with {}", userId, user); Validate.isTrue(userId == user.getId(), "userId doesn't match URL userId: " + user.getId()); userService.update(user); } @RequestMapping(value = "/{userId}", method = RequestMethod.DELETE) @ResponseStatus(value = HttpStatus.NO_CONTENT) public void delete(@PathVariable(value = "userId") long userId) { LOGGER.info("Deleting user with id {}", userId); userService.delete(userId); } @RequestMapping(method = RequestMethod.GET) @ResponseBody public UserList list() { LOGGER.info("Listing users"); return new UserList(new ArrayList<User>(userService.list())); } @ExceptionHandler(IllegalArgumentException.class) @ResponseStatus(HttpStatus.BAD_REQUEST) @ResponseBody public String handleClientErrors(Exception ex) { LOGGER.error(ex.getMessage(), ex); return ex.getMessage(); } @ExceptionHandler(Exception.class) @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR) @ResponseBody public String handleServerErrors(Exception ex) { LOGGER.error(ex.getMessage(), ex); return ex.getMessage(); } } Configure Spring. As you already observed, we used annotations all over, so Spring configuration is minimal (applicationContext.xml). <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xmlns:mvc="http://www.springframework.org/schema/mvc" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd"> <context:component-scan base-package="org.zmeu.blog.spring.rest" /> <mvc:annotation-driven /> </beans> Configure web application. Our web.xml configuration is also minimal. You can see that we only registered the Spring MVC DispatcherServlet and added the Log4jConfigListener for logging. <?xml version="1.0" encoding="UTF-8"?> <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <context-param> <param-name>log4jConfigLocation</param-name> <param-value>classpath:log4j.properties</param-value> </context-param> <listener> <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class> </listener> <servlet> <servlet-name>DispatcherServlet</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:applicationContext.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>DispatcherServlet</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> </web-app> Build the project. From command line, run mvn clean install command from the directory where pom.xml is located. Build must be successful. Deploy the resulted web application. Run mvn tomcat:run from command line from the same location. Test and consume RESTful services. Below you can see the class that is testing our RESTful services. I used TestNG testing framework (JUnit can be used as well). Tests that are shown below can be used as an example of how to consume RESTful services. All tests are disabled by default @Test(enabled = false). You have to enable them. This is done in order to skip tests execution at the build time. Tests should be run only after deploying the web application. In order to execute the tests, run mvn test command. package org.zmeu.blog.spring.rest.controller; import static org.testng.Assert.assertEquals; import static org.testng.Assert.assertTrue; import static org.testng.Assert.fail; import java.util.ArrayList; import java.util.Date; import java.util.List; import org.springframework.http.HttpStatus; import org.springframework.web.client.HttpClientErrorException; import org.springframework.web.client.RestTemplate; import org.testng.annotations.BeforeClass; import org.testng.annotations.Test; import org.zmeu.blog.spring.rest.domain.User; import org.zmeu.blog.spring.rest.domain.UserList; @Test(enabled = false) public class UserControllerTest { private static final String REST_SERVICE_URL = "http://localhost:8080/zmeu-blog-spring-rest/users"; private RestTemplate restTemplate; @BeforeClass protected void beforeClass() { restTemplate = new RestTemplate(); } public void create() { createAndAssertUser(); } public void read() { User createdUser = createAndAssertUser(); User user = restTemplate.getForObject(REST_SERVICE_URL + "/{userId}", User.class, createdUser.getId()); assertUser(user, createdUser); } public void update() { User user = createAndAssertUser(); user.setName("Updated user name"); restTemplate.put(REST_SERVICE_URL + "/{userId}", user, user.getId()); User updatedUser = restTemplate.getForObject(REST_SERVICE_URL + "/{userId}", User.class, user.getId()); assertUser(updatedUser, user); } public void updateIncorrectUrl() { User user = createAndAssertUser(); user.setName("Updated user name"); try { restTemplate.put(REST_SERVICE_URL + "/{userId}", user, user.getId() + 1); fail("Expecting HttpClientErrorException: 400 Bad Request"); } catch (HttpClientErrorException e) { assertEquals(e.getStatusCode(), HttpStatus.BAD_REQUEST); } } public void delete() { User createdUser = createAndAssertUser(); restTemplate.delete(REST_SERVICE_URL + "/{userId}", createdUser.getId()); try { restTemplate.getForObject(REST_SERVICE_URL + "/{userId}", User.class, createdUser.getId()); fail("Expecting HttpClientErrorException: 400 Bad Request"); } catch (HttpClientErrorException e) { assertEquals(e.getStatusCode(), HttpStatus.BAD_REQUEST); } } public void list() { UserList initialUsers = restTemplate.getForObject(REST_SERVICE_URL, UserList.class); User createdUser = createAndAssertUser(); UserList users = restTemplate.getForObject(REST_SERVICE_URL, UserList.class); List<User> createdUsers = new ArrayList<User>(users.getUsers()); createdUsers.removeAll(initialUsers.getUsers()); assertEquals(createdUsers.size(), 1); assertUser(createdUsers.get(0), createdUser); } private User createAndAssertUser() { User user = new User(); user.setId(0); user.setName("User name"); user.setRegistrationDate(new Date()); return createAndAssertUser(user); } private User createAndAssertUser(User user) { User createdUser = restTemplate.postForObject(REST_SERVICE_URL, user, User.class); assertUserNoId(createdUser, user); return createdUser; } private void assertUserNoId(User actual, User expected) { assertTrue(actual.getId() > 0); assertEquals(actual.getName(), expected.getName()); assertEquals(actual.getRegistrationDate(), expected.getRegistrationDate()); } private void assertUser(User actual, User expected) { assertTrue(actual.getId() > 0); assertEquals(actual.getName(), expected.getName()); assertEquals(actual.getRegistrationDate(), expected.getRegistrationDate()); } } Testing our RESTful services using web browser:

Retrieve user with id = 12

Retrieve user list Changing the representation of your resources from XML to JSON is very easy. No changes are required to be done in controllers or client side. You have to perform the following actions only: Add the following dependency to pom.xml: <dependency> <groupId>org.codehaus.jackson</groupId> <artifactId>jackson-mapper-asl</artifactId> <version>1.8.5</version> <scope>runtime</scope> </dependency> Remove all JAXB annotations from data-type classes (User.java and UserList.java) Taking an arbitrary Java object returned from a controller handler method and converting it into a client-pleasing representation is a job for one of Spring’s HTTP message converters. Spring comes with a variety of message converters: XML, JSON, Atom, RSS, binary, String, etc (see all classes implementing HttpMessageConverter). You are done! IMPORTANT: Although Spring 3 supports validation of arguments and return types for Spring MVC controllers using JSR-303 (Bean validation), it doesn’t work in case of RESTful controllers (see also bugs SPR-6709 and SPR-6928). Also you can have a look at the following related articles: A Comparison of Spring MVC and JAX-RS (from InfoQ). Using Spring 3.0 MVC for RESTful web services (describes some existing issues along with solutions). Spring 3 Type Conversion and Validation (from SpringSource TeamBlog) rest-based services with spring Configure Maven to generate classes from XML Schema using JAXB

Apache Commons project represents a set of reusable Java components. Apache Commons Lang is one of the Apache Commons components. It provides much needed additions to the standard JDK's java.lang package. One of its packages, org.apache.commons.lang3.builder contains a set of very useful builders that helps in creating consistent equals(), hashCode(), toString() and compareTo() methods. In this post, I will show how to generate equals(), hashCode(), toString() and compareTo() methods using Apache Commons Lang builders in Eclipse. For demonstrations I will use the latest stable release - Apache Commons Lang 3.0. Note that Lang 3.0 uses a different package (org.apache.commons.lang3) than its predecessors (org.apache.commons.lang). All the examples presented in this post will work also with the previous Apache Commons Lang releases; just change the package name from lang3 to lang. Native Support Eclipse supports out of the box generation of equals(), hashCode() and toString() methods. But only the generation of toString() can be configured to use different builders. Below is shown how to configure Eclipse to use ToStringBuilder to generate toString() methods. Prerequisites: Eclipse project is configured to include Apache Commons Lang jar in classpath. We have a class with 2 fields named string and number. Open Generate toString() wizard (from menu select Source ->

Generate toString()…). Choose Custom toString() builder option from Code Style drop down and press Configure… button as it is shown below.

Using Browse… button select org.apache.commons.lang3.builder.ToStringBuilder as Builder Class and press OK.

Press OK. Eclipse will generate the toString() method. It should look similar to this one: @Override public String toString() { ToStringBuilder builder = new ToStringBuilder(this); builder.append("string", string); builder.append("number", number); return builder.toString(); } Eclipse will save your settings, so next time you will not have to repeat these steps again. Just open Generate toString() wizard and hit OK. Custom Templates As I mentioned earlier, only toString() generation can be customized in Eclipse. Still, we can configure Eclipse to generate equals(), hashCode() and compareTo() using Apache Commons Lang builders by using Eclipse templates. Templates are little pieces of code with defined placeholders. Each template has a name, which serves as a shortcut to the template itself. You type the name, press CTRL + SPACE and it will be expanded. In order to access Eclipse templates open Window ->

Preferences and select Java ->

Editor ->

Templates. Now you can create new templates, edit existing ones or import directly ready templates.

Following is a list of templates that will allow you to generate equals(), hashCode(), compareTo() and even toString() using Apache Commons Lang builders. hashCode() template @Override public int hashCode() { ${builderType:newType(org.apache.commons.lang3.builder.HashCodeBuilder)} ${builder:newName(builderType)} = new ${builderType}(); ${builder}.append(${field});${cursor} return ${builder}.toHashCode(); } This is how it will look like in Eclipse:

equals() template @Override public boolean equals(Object obj) { if (this == obj) { return true; } if (obj == null) { return false; } if (!(obj instanceof ${enclosing_type})) { return false; } ${enclosing_type} other = (${enclosing_type}) obj; ${builderType:newType(org.apache.commons.lang3.builder.EqualsBuilder)} ${builder:newName(builderType)} = new ${builderType}(); ${builder}.append(${field}, other.${field});${cursor} return ${builder}.isEquals(); } compareTo() template @Override public int compareTo(${enclosing_type} o) { ${builderType:newType(org.apache.commons.lang3.builder.CompareToBuilder)} ${builder:newName(builderType)} = new ${builderType}(); ${builder}.append(${field}, o.${field});${cursor} return ${builder}.toComparison(); } toString() template @Override public String toString() { ${builderType:newType(org.apache.commons.lang3.builder.ToStringBuilder)} ${builder:newName(builderType)} = new ${builderType}(this, ${:newType(org.apache.commons.lang3.builder.ToStringStyle)}.${DEFAULT_STYLE}); ${builder}.append("${field}", ${field});${cursor} return ${builder}.toString(); } Also you can easily import all the above templates using Import… button from the following file eclipse-templates-apache-commons.xml. After you defined the templates, you can start using them through Content Assist (CTRL + SPACE). Start typing the name of template in editor and then press CTRL + SPACE. Choose the required template and press ENTER.

Customize the variables names and fields that should be included in the builder. Append more fields if it’s required. You have to get at the end something like this: @Override public int hashCode() { HashCodeBuilder builder = new HashCodeBuilder(); builder.append(number); builder.append(string); return builder.toHashCode(); } End.

A nice thing about parameterized classes in Java is that you can extract and access information about class type arguments at runtime (for an explanation about parameters and arguments see Parameters and arguments). Let’s say that we have an abstract parameterized superclass that has a method which provides some common functionality to all its subclasses. And inside that method we wanted to know what is the class type argument specified by the subclass. public abstract class GenericAbstractSuperclass<T> { public void foo() { // here we wanted to know what is the class type argument } } public class GenericClass1 extends GenericAbstractSuperclass<Integer> { // subclass methods } public class GenericClass2 extends GenericAbstractSuperclass<String> { // subclass methods } In above example, method foo() has to access class type argument. In case of GenericClass1 it has to get Integer and in case of GenericClass2 it has to get String. Below is listed a utility class that can accomplish this. /** * Generics utility class. * * @author Andrei Zagorneanu * @since 2011-07-31 * @see <a href="http://azagorneanu.blogspot.com">http://azagorneanu.blogspot.com</a> */ public class Generics { private Generics() { // empty, in order to avoid instantiation } public static <T> Class<T> extractTypeArgumentFromClass(Class<?> parameterizedClass) throws IllegalArgumentException { return extractTypeArgumentFromClass(parameterizedClass, 0); } public static <T> Class<T> extractTypeArgumentFromClass(Class<?> parameterizedClass, int argumentNumber) throws IllegalArgumentException { ParameterizedType parameterizedType = extractParameterizedTypeFromClass(parameterizedClass); if (parameterizedType == null) { throw new IllegalArgumentException( "Class and any of its superclasses are not parameterized."); } return (Class<T>) getActualTypeArgument(parameterizedType, argumentNumber); } private static Type getActualTypeArgument(ParameterizedType parameterizedType, int argumentNumber) throws IllegalArgumentException { Type[] typeArguments = parameterizedType.getActualTypeArguments(); if (typeArguments.length == 0) { throw new IllegalArgumentException("Class is not parameterized."); } if (argumentNumber < 0 || typeArguments.length <= argumentNumber) { throw new IllegalArgumentException("Invalid argumentNumber."); } return typeArguments[argumentNumber]; } public static ParameterizedType extractParameterizedTypeFromClass(Class<?> parameterizedClass) { Type genericSuperclass = parameterizedClass.getGenericSuperclass(); if (genericSuperclass instanceof ParameterizedType) { return (ParameterizedType) genericSuperclass; } if (genericSuperclass != null) { return extractParameterizedTypeFromClass((Class<?>) genericSuperclass); } return null; } public static <T> Class<T> extractTypeArgumentFromInterface(Class<?> parameterizedClass) throws IllegalArgumentException { return extractTypeArgumentFromInterface(parameterizedClass, 0); } public static <T> Class<T> extractTypeArgumentFromInterface(Class<?> parameterizedClass, int argumentNumber) throws IllegalArgumentException { ParameterizedType parameterizedType = extractParameterizedTypeFromInterface(parameterizedClass); if (parameterizedType == null) { throw new IllegalArgumentException( "Class and any of its interfaces are not parameterized."); } return (Class<T>) getActualTypeArgument(parameterizedType, argumentNumber); } private static ParameterizedType extractParameterizedTypeFromInterface( Class<?> parameterizedClass) { Type[] genericInterfaces = parameterizedClass.getGenericInterfaces(); for (Type genericInterface : genericInterfaces) { if (genericInterface instanceof ParameterizedType) { return (ParameterizedType) genericInterface; } ParameterizedType parameterizedType = extractParameterizedTypeFromInterface((Class<?>) genericInterface); if (parameterizedType != null) { return parameterizedType; } } return null; } } This class provides methods for extracting type arguments from classes and from interfaces as well. The only use case which is not supported directly is when a class extends from a superclass that implements a parameterized interface. In this case, you will not be able to extract type argument from the class directly. Still, you can extract the class type argument using extractTypeArgumentFromInterface(parameterizedClass.getSuperclass()). Here, we first extracted the superclass and then we used it to extract the type argument from its interface. Class source code can be found here. Unit tests source code can be found here. Unit tests represent also a good example of class usage. Update (07-Aug-2011): Recently a new major release of Apache Commons Lang was released - Apache Commons Lang 3.0. Among new utility classes that were added, you will find a new TypeUtils class, which provides utility methods for working with generic types (including retrieval of type arguments from parameterized classes).

If you are a Blogger user, then you already know that currently there is no possibility to upload your custom JavaScript and CSS files. You have to host your files somewhere else and then link them in your blog template. One of the places where you can host your custom JavaScript, CSS and any type of files is Google Code. Google Code, is a free platform to host Open Sources Projects. You can just simply upload your files and hotlink to them. Main issue in this simple task is that it’s working for JavaScript files but it doesn’t work when hot linking to CSS or Image files. The reason is that, by default when we upload any file to Google Code, it is served as text-plain mime-type. This works with JavaScript files but not with CSS, Image files or HTML files. Below is a small tutorial showing how to create a new project on Google Code, how to use an SVN client to upload new files to it and how to set the mime-type for these files. Go to http://code.google.com/hosting/ and create a new Google Code project in case you don’t have one already.

Make sure that you have selected Subversion as Version Control system.

Note down your repository URL, username and password. We will need these details in the next steps when we will use an SVN client to upload files to repository.

Install an SVN client. In this example we are using TortoiseSVN. Right click where ever you are working on Windows Explorer and lunch TortoiseSVN Repo-browser.

Enter you repository URL, then username and password (from step no. 3).

Repo-browser lets you browse, add, remove and edit files from your SVN repository.

After you have uploaded the files to repository, you can set their mime-type. Right-click on a file and select Show properties from context-menu.

Using Properties dialog you can add, remove and edit file’s properties.



You are done uploading. Get the file URL by doing left click on the file you want to hot link from the repository browser and select and copy the URL. Just replace the https with http and you are done. Now you have got the URL to hot link. Use it where ever you like.

I want to say from the beginning that I'm not a designer and I never had such skills, but still I decided to make some buttons for Java Applet and Java Web Start. You can see below what I did:

 

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