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...

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.*; ...

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.

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.

In this simple example, I create a simple validating bean and create a JUnit test to test the validation. The bean ( src/main/java/com/example/Person.java ): package com.example; import javax.validatio... The test ( src/test/java/com/example/TestPerson.java ): package com.example; import java.util.Set; ... Run the test: mvn clean test You'll notice that one test passed and the other failed. The tests require that a person must have a name and the name cannot be empty, so @NotNull is not the right rule to use here. To make sure that the name is not empty, we need to use @Pattern . But since a null String matches any pattern, @NotNull is also needed: package com.example; import javax.validatio...

Mapping Java objects to Jackson JSON is pretty simple. But if you name a JSON field wrong, you'll get the "Unrecognized field ... (Class ...), not marked as ignorable" error. The rule for mapping a Java bean attribute name to a JSON field name is: lower all leading capital letters until the first lower case letter . For example, this Java class: package com.example; public class Person { ... maps to this JSON string: { "firstName": "Jane", "lastName": "... Test code: package com.example; import java.net.URL; ...

This is a simple JSP custom tags library with tag body. Just like the JSF counterpart , it splits a string and repeats the body for each word, i.e., with this markup: <%@ taglib uri="http://custom.tag.com/demo" prefix... output: <html> <body> <p>Hello Tigger!</p> <p>H... With Maven, this is the directory structure: ./src ./src/main ./src/main/resources ./s... There are three files to write: pom.xml : <project xmlns="http://maven.apache.org/POM/4.0.0"... src/main/java/tagdemo/IterateTag.java : package tagdemo; import java.io.IOException... src/main/resources/META-INF/demotag.tld : <?xml version="1.0" encoding="UTF-8"?> <!DO... Build with: mvn clean install To use it as a dependency in other Maven projects: <dependency> <groupId>tag-demo</groupId> ...

You can add custom implicit variables to JSF pages by using a custom EL resolver, in two simple steps: Write an ELResolver class to resolve the variable Add the ELResolver to faces-config.xml Starting from the Maven Hello World example: Add faces API and EL dependencies to pom.xml : <dependencies> <dependency> <groupId>o... Add a simple greeter class ( src/main/java/com/example/Greeter.java ): package com.example; public class Greeter {... Add our custom EL resolver ( src/main/java/com/example/ELResolver.java ): package com.example; import java.util.Itera... Add the custom EL resolver to src/main/resources/META-INF/faces-config.xml <?xml version="1.0" encoding="UTF-8"?> <faces-c... Build JAR with mvn package Drop the JAR into WEB-INF/lib of a webapp and test the new EL with: <h:outputText value="#{Greeter.sayHi('Mike')}"/> Fixed: the setValue method used to throw an exception, which is wrong. @Override public void setValue(ELContext ctx, O......