Scaling an image with default Java API loses quality (horribly!): public static BufferedImage resizeImage(Buffer... The imgscalr library does the job beautifully. And its' very easy to do: // import org.imgscalr.Scalr; public static... To import the library in Maven: <dependency> <groupId>org.imgscalr</groupId> ...

To implement a JSP custom tag with dynamic attributes (for example, to pass-thru arbitrary attributes not handled by the JSP tag): Set the dynamic-attributes element to true in the TLD: <tag> <name>mark</name> <tag-class>c... The tag handler must implement javax.servlet.jsp.tagext.DynamicAttributes : package com.example.jsp; import java.io.*; ...

Step 1: create a Json factory: package com.my.service.dev; import java.io.... Step 2: use it: ObjectMapper mapper = new ObjectMapper(new AllowCo...

Spring MVC 3.1 can send either JSON or HTML response on the same URL, depending on the type of response requested. With this mechanism, a page can be sent when directly requested from a link, but a JSON response can be sent in response to an AJAX request. This is the controller code: package com.example; import java.util.Map; ... In the above example, JSON response will be sent when the HTTP request contains header "Accept: application/json". HTML response will be sent then the header is "Accept: */*", or "Accept: text/html", or anything else. You can add a limitation that the HTML response does not produce "application/json". But then the question is which response will be sent when the HTTP header is "Accept: */*"? Both methods will...

After a user resets a password, I want to force the user to change the password before she gets access to secured content. This is usually done with a servlet filter. But with Spring MVC, you can also use a HandlerInterceptor . According to Spring JavaDoc: HandlerInterceptor is basically similar to a Servlet 2.3 Filter, but in contrast to the latter it just allows custom pre-processing with the option of prohibiting the execution of the handler itself, and custom post-processing. Filters are more powerful, for example they allow for exchanging the request and response objects that are handed down the chain. Note that a filter gets configured in web.xml, a HandlerInterceptor in the application context. As a basic guideline, fine-grained handler-related preprocessing tasks are candidates...

This example creates an instance of XMLGregorianCalendar and converts it to java.util.Date : import java.util.Date; import javax.xml.datatyp...

In the bean validation API javadoc, for every constraint annotation, there's a corresponding .List annotation. For example, for @NotNull , there's @NotNull.List , for which JavaDoc says: Defines several @NotNull annotations on the same element What would you accomplish with multiple @NotNull annotations that you cannot accomplish with one @NotNull ? This is a test to reveal some of the facts. Change the Person class to: package com.example; public class Person { ... Add another JUnit test ( src/test/com/example/TestPersonWithList.java ): package com.example; import java.util.Itera... As the test shows, a Person bean can never be valid because we are requiring that name must begin with Mr and Ms . One might think that the same can be accomplished by simply repeating the @Pattern annotation multiple times,...

Validation groups can be used to control which rules validation rules to run. A validation group can be identified by any Java interface (not class!). Multiple validation groups may be specified when validating. In this example, I added a validation group named MyValidationGroup ( src/main/java/com/example/MyValidationGroup.java in Maven project): package com.example; public interface MyVal... and added a @Size rule for a person's name, because my database can only store up to 15 characters for a person's name: package com.example; import javax.validatio... Now validate Person with a JUnit test ( src/test/java/com/example/TestPersonWithGroup.java in Maven project): package com.example; import java.util.Set; ... Test with " mvn clean test ". The rules where groups is not specified, which belong to the javax.validation.groups.Default group, are not executed with these tests.

A bean class may also be defined through composition. The validation rules of referenced beans are not automatically called when a composite bean is validated. You need to use the @Valid annotation to trigger cascade validation. As an example, I create a class named AccountPerson2 , which contains a Person with the addition of an email field ( src/main/java/com/example/AccountPerson2.java in Maven project): package com.example; import javax.validatio... Now validate AccountPerson2 with a JUnit test ( src/test/java/com/example/AccountPerson2Test.java in Maven project): package com.example; import java.util.Set; ... Test with " mvn clean test " and you'll see that the validation rules of the Person class are executed when an AccountPerson2 bean is validated. Without the @Valid annotation, the validation rules of Person will not be called.

When a bean class inherits another class, the validation rules of the parent class is automatically executed when a child class bean is validated. As an example, I create a class named AccountPerson , which inherits the Person class with the addition of an email field ( src/main/java/com/example/AccountPerson.java in Maven project): package com.example; import javax.validatio... Now validate AccountPerson with a JUnit test ( src/test/java/com/example/AccountPersonTest.java in Maven project): package com.example; import java.util.Set; ... Test with " mvn clean test " and you'll see that the validation rules of the Person class are executed when an AccountPerson bean is validated.