First, the test command that sleeps random number of seconds ( sleeper.sh ): #!/bin/bash stime=$[$RANDOM % 20] sleep $sti... As comparison, synchronous pipe code: #include <sys/wait.h> #include <stdio.h> #in... Asynchronous pipe code: #include <sys/wait.h> #include <stdio.h> #in...

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...

Suppose that I have an email field annotated with: @NotEmpty(message="Please enter email address") ... Bean validation will trigger two errors when no email address is entered: the email field is empty an empty email field is not a valid email address Displaying both errors to the user with <form:errors> would be redundant and confusing: <%@ taglib uri="http://www.springframework.org/tag... This is how to display the first error only: <spring:bind path="emailAddress"> <c:if test="$...

If forgotPasswordForm.error is a String and not null, you cannot test the error condition with: <!-- This does not work! --> <c:if test="${forg... You have to use "not empty": <c:if test="${not empty forgotPasswordForm.error}"...

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.

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; ...