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In general a REST service serves JSON document formats. In Spring Boot it is even the standard without having to configure anything. Over HTTP we have the ability to send a Content-Type as header to instruct the server to return a certain document format (Mime type). Besides handling JSON, XML is another common document format. But what if we want to serve or read a YAML document format? This tutorial provides the required steps to be able to handle objects in YAML format. To be able to send a YAML Content-Type with the header, and to be able to serialize and deserialize with the existing ObjectMappers of Jackson. This tutorial will use Spring Boot, Jackson and a YAML dataformat extension library for Jackson.

First we need to add the YAML Jackson extension to our Gradle build file.

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The default JSON error body of Spring Boot can be customized or extended by defining our own ErrorAttributes implementation. In Spring Boot we get an error response JSON format for free. Any thrown Exception is automatically translated to this JSON format and returned with a corresponding HTTP status.

As soon as we throw an Exception in a @RequestMapping annotated method of a @Controller, the thrown Exception is translated to a HTTP status and a JSON error body. The default JSON error body looks like:

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In Spring we use the @EnableAutoConfiguration each time when we use the @SpringBootApplication annotation. If we look at the @SpringBootApplication we can see that this automatically enables the @EnableAutoConfiguration. This last mentioned annotation triggers all the auto-configuration enabled configurations on the classpath. We can write an auto-configuration enabled @Configuration ourself in only two steps.

package com.jdriven.example;

import org.springframework.context.annotation.Configuration;

@Configuration
public class MyOwnAutoConfiguration {

    //You can define your own beans here and
    //further setup this Configuration as you normally would do

}

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In Spring MVC we get some method argument types resolved by default and injected in Spring MVC controller methods. Some examples are Model, Locale and OutputStream. What if we want to inject a custom argument in Spring MVC controller methods? In this example we extract the X-Application-Version HTTP header from the request and inject that as a method argument called version. Our controller class will look like the following:

@RestController
public class MyController {

    @RequestMapping("/persons")
    //I want the version to be automatically injected
    public List getPersons(String version) {
        .....
        return someList;
    }
} 

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Recently I wanted to use the Tuckey UrlRewriteFilter. It is described as: A Java Web Filter for any compliant web application server, which allows you to rewrite URLs before they get to your code.

I wanted to load my urlrewrite.xml as a Spring (classpath) resource, instead of loading it from the default location provided by the UrlRewriteFilter. The default behavior loads the configuration file from /WEB-INF/ulrewrite.xml. In my case I wanted to load it from the /src/main/resources folder, which is the root of my classpath.

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I would like to show different ways of using Spring's @Autowired annotation: Constructor, Method and Field autowiring.
The examples I show are all a form of byType autowiring mode (constructor autowiring mode is Analogous to byType). Take a look at the Spring Reference guide for more information on the Autowiring modes.

Create a constructor with a dependent bean as constructor parameter and add the @Autowired annotation to the constructor. A big advantage of autowiring by constructor is that the field can be made final, and therefore may not be changed after construction.

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We have to deal with legacy code, even when we would like to use the best and newest technologies available. Imagine the new code is written with the newest technologies of the Spring Framework and the legacy code is not written in Spring at all. Then using Spring managed Beans in non-managed Spring objects is one of the patterns we have to deal with. The legacy code has non-managed Spring objects, while the code we want to reference to is a Spring managed Bean. How do we solve this problem?

Let's assume we have a managed Spring Bean called TaxService and an object called LegacyObject. The LegacyObject is the legacy code from where we would make a reference to the method calculateTax on the managed Spring Bean.

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So many men, so many minds. When we are implementing software for different customers we sometimes need to handle various requirements for the same project. For example Customer A needs SAML authentication and customer B needs LDAP authentication. With Spring Profiles (available from Spring 3.1) we are able to provide a way to segregate parts of our implemented application configuration. This blog will help us to make certain code or rather certain Spring beans only available for specific requirements. For example the example used in this blog can be used to activate the required authentication provider for the provider manager when using Spring Security. Profiles can be configured by annotations and/or by xml. Annotations @Component or @Configuration annotated beans can contain the annotation @Profile to only load them in a certain environment.

@Component
@Profile("ldap")
public class LDAPAuthentication {
   public LDAPAuthentication() {
      System.out.println("LDAP Authentication set by annotations");
   }
}

@Component
@Profile("saml")
public class SAMLAuthentication {
   public SAMLAuthentication() {
      System.out.println("SAML Authentication set by annotations");
   }
}

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While writing unit tests, you often have to mock dependencies like services or controllers. Often  a constructor is used to autowire the dependencies as shown in the example below. In the Test class I instantiated the ContactService using a contactRepository Mock object

@Service
public class ContactServiceImpl implements ContactService {

private final ContactRepository contactRepository;

    @Autowired
    public ContactServiceImpl(final ContactRepository contactRepository) {
    this.contactRepository = contactRepository;
    }

    public void saveContact(final Contact contact) {
    contactRepository.save(contact);
    }
}

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