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> ...

This is a utility to convert a byte array to hex string, and to convert a hex string back to the original. To convert a String to hex, you must call String.getBytes() first. The utility does not pretend to know your string encoding. public class StringHexUtil { public static ... This also works: String binaryToHex(byte[] data) { StringBui...

There are two steps to create a custom function for JSP: Declare the function in the TLD: <?xml version="1.0" encoding="UTF-8" ?> <taglib... Implement the function (must be static): package com.example; public class UrlTransl... To use the function: <%@ taglib uri="http://www.example.com/jsp/tags" p...

Simply call pageContext.setAttribute() to export a variable from within a JSP custom tag: public class MyCustomVarTag extends TagSupport { ... The availability of the exported variable can be limited in the TLD: <tag> <name>setVar</name> <tag-class... The availability scopes are: Value Availability NESTED Between the start tag and the end tag. AT_BEGIN From the start tag until the scope of any enclosing tag. If there’s no enclosing tag, then to the end of the page. AT_END After the end tag until the scope of any enclosing tag. If there’s no enclosing tag, then to the end of the page.

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,...