Develop Reference

How to Load an Entity Inside a Spring Data REST Server by Self Link?

Given a Spring Data REST (SDR) server built with Spring Boot Gradle Plugin 2.2.5.RELEASE, is it possible to load an #Entity by self link within the server application?
I'm aware how to access it with an HTTP client, e.g. using curl:
$ curl localhost/users/1 # Responds with 200 OK and JSON representation
What I'm searching for is a mechanism to do this in the server using Java only, ideally using a standard SDR mechanism:
#Service
public class SelfLinkResolver {
public Object findBySelfLink(Link self) {
if (self == null || !self.getRel().equals(SELF)) {
throw new IllegalArgumentException("Non-null self link expected");
}
return null; // How to return the entity using a standard SDR mechanism?
}
public void exampleCall() {
Link self = new Link("localhost/users/1");
Object entity = findBySelfLink(self);
requireNonNull(entity, "Failed to load entity by self link");
}
}

An internal solution is parse your link and extract the ID (1 in your example), the call repository.findById(id).
Another solution would be new a RestTemplate, call your own API.

I finally came up with this solution, which uses SDR's UriToEntityConverter. In contrast to my question, it requires not only the self link, but also the entity class. It therefore doesn't fully answer my initial question.
I guess that there is no SDR solution that does not require the entity class, since there is no need for this within the framework, at least for usual API calls. SDR is always provided with the type information through the Repository, to which the self link refers. However, I didn't dive into other classes such as PersistentEntities, RepositoryInvokerFactory or Repositories, which might provide a solution for this.
WARNING: My tested implementation differs from this. This code is untested, but should illustrate the idea.
import lombok.NonNull;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.data.mapping.context.PersistentEntities;
import org.springframework.data.repository.support.Repositories;
import org.springframework.data.repository.support.RepositoryInvokerFactory;
import org.springframework.data.rest.core.UriToEntityConverter;
import org.springframework.hateoas.Link;
import org.springframework.stereotype.Component;
import java.net.URI;
import java.util.Optional;
import static com.google.common.base.Preconditions.checkArgument;
import static java.lang.String.format;
import static org.springframework.hateoas.IanaLinkRelations.SELF;
#Component
public class SelfLinkToEntityConverter extends UriToEntityConverter {
private static final TypeDescriptor URI_DESCRIPTOR = TypeDescriptor.valueOf(URI.class);
SelfLinkToEntityConverter(#NonNull PersistentEntities entities,
#NonNull RepositoryInvokerFactory invokerFactory,
#NonNull Repositories repositories) {
super(entities, invokerFactory, repositories);
}
#NonNull
public <T> Optional<T> findBySelfLink(#NonNull Link self, #NonNull Class<T> entityClass) {
checkArgument(self.getRel().equals(SELF), "Non-null self link expected");
URI uri = self.expand().toUri();
TypeDescriptor typeDescriptor = TypeDescriptor.valueOf(entityClass);
try {
#SuppressWarnings("unchecked")
T entity = (T) super.convert(uri, URI_DESCRIPTOR, typeDescriptor);
return Optional.ofNullable(entity);
} catch (IllegalArgumentException o_O) {
throw new IllegalArgumentException(format("Failed to load %s: %s",
entityClass.getSimpleName(), self.getHref()));
}
}
}

use of custom annotations

I found several related (not duplicate) question to this, but they didn't satisfy me.
I am unable to understand where and why to use custom annotations?
I read an example of custom annotation in a book, but it was not explained thoroughly.
#interface MyAnno
{
String str();
int val();
}
class MyClass
{
#MyAnno(str = "Annotation example", val = 100)
public static void myMeth()
{
System.out.println("Inside myMeth()");
}
}
class CustomAnno
{
public static void main(String args[])
{
MyClass.myMeth();
}
}
The output is as expected Inside myMeth().
I am having few questions regarding this example.
1- How can I use String str() and int val() in this program? OR
What is the use of any abstract method of an custom annotation?
2- Why custom annotations. I mean that what effect they are having on any code.
3- How can I create an annotation which is having effects like #override is having?(I mean any kind of effect which can be noticed)
If this example is useless for you, then please give me a suitable small example in which a custom annotation is used.

Three main reasons to use custom annotations are:
To reduce the effort of writing code (a compile-time annotation processor generates code for you). Here is a tutorial: part 1, part 2.
To provide additional correctness guarantees (a compile-time annotation processor warns you about errors). One nice tool for this is the Checker Framework, which prevents null pointer dereferences, concurrency errors, and more.
To customize behavior (at run time, your code checks for the annotation using reflection and behaves differently depending on whether the annotation is present). Frameworks such as Hibernate use annotations this way; also see an Oracle article.
In each case, use of annotations reduces the likelihood of errors in your code, compared to other non-annotation approaches.

Here is a minimal example. The following code demonstrates use of custom annotation.
It is about Employees and Benefits. If we have a requirement such that BasicBenefits has to be applied to all types of employess then we can come up with custom annotation such as BasicBenefits, and annotate all types of Employee implementations (e.g. CorporateEmployee, ContractEmployee, ManagerEmployee etc. etc.) with the BasicBenefits.
Custom Annotation Class(interface)
import java.lang.annotation.*;
#Inherited
#Documented
#Target(ElementType.TYPE)
#Retention(RetentionPolicy.RUNTIME)
#interface BasicBenefits {
String bId() default "B-101";
String bName() default "General Class A Employee";
}
Class using the custom annotation(no need of any imports):
#BasicBenefits(bId="B-400", bName="General Plus Class A Employee")
public class Employee {
String eId;
String eName;
public Employee(String eId, String eName){
this.eId = eId;
this.eName = eName;
}
public void getEmployeeDetails(){
System.out.println("Employee ID: "+eId);
System.out.println("Employee Name: "+eName);
}
}
Driver class to test out the above.
import java.lang.annotation.Annotation;
public class TestCustomAnnotationBasicBenefits {
public static void main(String[] args) throws Exception{
Employee emp = new Employee("E-100", "user3320018");
emp.getEmployeeDetails();
Class reflectedClass = emp.getClass();
Annotation hopeBenefitAnn = reflectedClass.getAnnotation(BasicBenefits.class);
BasicBenefits bBenefits = (BasicBenefits)hopeBenefitAnn;
System.out.println("Benefit ID: "+bBenefits.bId());
System.out.println("Benefit Name: "+bBenefits.bName());
}
}
Your code look almost there, just two things need to be included in the main method.
1.) Need reference to MyClass
2.) Need to get the annotation using reflection from MyClass.
Here is a bit modified code from what you have:
#Inherited
#Documented
#Target(ElementType.TYPE)
#Retention(RetentionPolicy.RUNTIME)
#interface MyAnno
{
String str();
int val();
}
//using above custom annotation on class level
//can also use method level
//just need to change t #Target(ElementType.METHOD)
#MyAnno(str = "Annotation example", val = 100)
class MyClass
{
public static void myMeth()
{
System.out.println("Inside myMeth()");
}
}
import java.lang.annotation.Annotation;
class CustomAnno
{
public static void main(String args[])
{
//1. getting reference to the class where the custom annotation is applied.
//2. then getting the annotation to get the values
MyClass myClass = new MyClass();
Class cls = myClass.getClass();
Annotation getMyAnno = cls.getAnnotation(MyAnno.class);
MyAnno myAnno = (MyAnno)getMyAnno;
MyClass.myMeth(); //left this as is.
System.out.println("myAnno.str(): "+ myAnno.str());
System.out.println("myAnno.str(): "+ myAnno.val());
}
}

The abstract methods of the annotation define the values you can pass to it (in your case str = "Annotation example", val = 100). You can access them using reflection (Method.<T>getAnnotation(Class<T>)). Custom annotations don’t have direct impact. They are only useful if you evaluate them.
Note that you have to annotate your custom annotation with #Retention(value=RUNTIME) to be able to read it via reflection.

To be of any use, annotations must be parsed first. The built-in annotations (such as #Override or #FunctionalInterface, to name the most obvious ones) are parsed by the compiler itself. As for custom annotations, these guys are commonly parsed by third-party frameworks, although we can also use the reflection mechanism to demonstrate this technique in standalone code.
By way of an example, the code below changes its behaviour at run time depending on the value of the field declared in the custom annotation named #SwitchingAnnotation:
import java.lang.annotation.Target;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
#Target(ElementType.METHOD)
#Retention(RetentionPolicy.RUNTIME)
#interface SwitchingAnnotation{
boolean flag();
}
public class Worker{
void doThis(){ System.out.println("Doing this"); }
void doThat(){ System.out.println("Doing that"); }
#SwitchingAnnotation(
flag = false
)
public void work(boolean flag) {
if (flag) doThis();
else doThat();
}
}
class Test{
public static void main(String[] args) {
try{
SwitchingAnnotation sw = Worker.class.getMethod("work", boolean.class)
.getAnnotation(SwitchingAnnotation.class);
new Worker().work(sw.flag()); // prints Doing that
}
catch(NoSuchMethodException nsme){
System.out.println(nsme);
}
}
}

How would I write an automated check that every parameter has a specific annotation?

I'm writing a Rest API and my automated tests are calling the class directly without deploying the to the server. As an example, I am testing this method:
#GET
#Path("/{referenceId}")
#Produces("application/json")
public String findByReferenceId(#PathParam("referenceId") String referenceId,
String view) {
My tests are checking that the logic works and they pass. But this code has a bug: I forgot to put a #QueryParam annotation on that view parameter. So this code works when tested, but if you try to use this resource on the deployed app, the view parameter will never be settable.
There are many ways I can solve this, but my current preference is to somehow write an automated check that if a method has a #Path annotation, then every parameter must have either a #PathParam, a #QueryParam or whatever other valid annotation can be there.
I prefer this over a new end-to-end test, because my other tests are already covering 95% of that logic. I just don't know how to automate this check. I'm using Maven and CXF (which means I'm using Spring). I'm hoping there's a plugin that can be configured to do this.
Something I just realized: It's valid to have a single parameter without an annotation. When you do this, jax-rs sets it to the entity you pass in. I'm not sure how to deal with this scenario. I could create my own custom annotation called #Payload and tell people to use it, but something seems wrong about that.

Here's my solution. In the end, I decided to create a #RawPayload annotation. Otherwise, I can't know if the missing annotation is intentional or not. Here's where I got the Reflections class: https://code.google.com/p/reflections/
import org.junit.Test;
import org.reflections.Reflections;
import org.reflections.scanners.MethodAnnotationsScanner;
import javax.ws.rs.Path;
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.util.Set;
import static org.junit.Assert.assertTrue;
...
#Test
public void testAllParametersAreAnnotated() throws Exception {
String message = "You are missing a jax-rs annotation on a method's parameter: ";
Reflections reflections = new Reflections("package.for.my.services", new MethodAnnotationsScanner());
Set<Method> resourceMethods = reflections.getMethodsAnnotatedWith(Path.class);
assertTrue(resourceMethods.size() > 0);
for (Method resourceMethod : resourceMethods) {
for (int i = 0; i < resourceMethod.getGenericParameterTypes().length; i++) {
Annotation[] annotations = resourceMethod.getParameterAnnotations()[i];
boolean annotationExists = annotations.length > 0;
assertTrue(message +
resourceMethod.getDeclaringClass().getCanonicalName() +
"#" +
resourceMethod.getName(),
annotationExists && containsJaxRsAnnotation(annotations));
}
}
}
private boolean containsJaxRsAnnotation(Annotation[] annotations) {
for (Annotation annotation : annotations) {
if (annotation instanceof RawPayload) {
return true;
}
if (annotation.annotationType().getCanonicalName().startsWith("javax.ws.rs")) {
return true;
}
}
return false;
}
Here's my annotation:
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
/**
* I'm creating this marker so that we can put it on raw payload params. This is normally unnecessary,
* but it lets me write a very useful automated test.
*/
#Retention(RetentionPolicy.RUNTIME)
public #interface RawPayload {
}

How to test java code that uses Basho's riak-java-client?

I'm creating a small java service that returns a list of restaurants depending on the selected place.
Data is retrieved from Riak using com.basho.riak:riak-client:2.0.0 and the read operation is wrapped in a TenacityCommand.
Important classes are described below and I would be happy if you could assist me in creating a solid and simple unit test.
Commands are created using a factory:
package service.command.factory;
import com.basho.riak.client.api.RiakClient;
import com.basho.riak.client.api.commands.kv.FetchValue;
import com.basho.riak.client.core.query.Location;
import com.basho.riak.client.core.query.Namespace;
import domain.Place;
import service.command.FetchRestaurantsCommand;
public class FetchRestaurantsCommandFactory {
private final RiakClient riakClient;
private final Namespace namespace;
public FetchRestaurantsCommandFactory(final RiakClient riakClient, final Namespace namespace) {
this.riakClient = riakClient;
this.namespace = namespace;
}
public FetchRestaurantsCommand create(final Place place) {
Location location = new Location(namespace, place.getName());
FetchValue riakCommand = new FetchValue.Builder(location).build();
return new FetchRestaurantsCommand(riakClient, riakCommand);
}
}
And the command looks like this:
package service.command;
import java.util.Optional;
import service.command.keys.WhereToEatDependencyKeys;
import com.basho.riak.client.api.RiakClient;
import com.basho.riak.client.api.commands.kv.FetchValue;
import com.basho.riak.client.api.commands.kv.FetchValue.Response;
import com.yammer.tenacity.core.TenacityCommand;
import domain.Restaurant;
import domain.RestaurantList;
public class FetchRestaurantsCommand extends TenacityCommand<Optional<RestaurantList>>{
private final RiakClient riakClient;
private final FetchValue fetchValue;
public FetchRestaurantsCommand(RiakClient riakClient, FetchValue fetchValue) {
super(WhereToEatDependencyKeys.RIAK_GET_RESTAURANTS);
this.fetchValue = fetchValue;
this.riakClient = riakClient;
}
#Override
protected Optional<RestaurantList> run() throws Exception {
Response response = riakClient.execute(fetchValue);
return Optional.ofNullable(response.getValue(RestaurantList.class));
}
#Override
protected Optional<RestaurantList> getFallback() {
return Optional.of(RestaurantList.createFallback(new Restaurant("My failure suggestion")));
}
}
The above classes are used like:
Place place = // Created from url parameter
RiakClient riakClient = // created on start using the app's conf
Namespace namespace = // created on start using the app's conf
FetchRestaurantsCommandFactory factory = new FetchRestaurantsCommandFactory(riakClient, namespace);
FetchRestaurantsCommand command = factory.create(place);
return command.execute();
Apart from the features provided by TenacityCommand, how should I assert that my system fetches data as expeceted?
My initial idea was to mock a RiakClient to return a predefined FetchValue.Response and then make assertions on the resulting RestaurantList.
Unfortunately its not possible to instantiate or Mockito.mock a FetchValue.Response due to its design.
The accepted answer in How to mock riak java client? describes why Mockito won't work.

As far a I understood you want to write unit test. So you want to test that assuming some Response whether Optional<RestaurantList> instance is constructed correctly or not.
What I can think of is to wrap riakClient.execute(fetchValue); in a protected (or package private) helper function like:
Response fetch() {
return riakClient.execute(fetchValue);
}
Then in your test you can inherit from FetchRestaurantsCommand and override fetch function by returning any Response
Now, you can write any test to see whether the conversion of given Response to Optional<RestaurantList> behaves as expected or not.
If you need entire code and my explanation is not clear enough let me know to provide it.

I ended up using PowerMock as suggested by #gontard. See my unit test on GitHub: FetchRestaurantsCommandTest.java
I considered to create a fake/mock RiakClient in the com.basho.riak.client package. Such class could hopefully instantiate the Response object in the same way as the real client does. It would probably work for fetchValue but it would grow too big when involving more advanced Riak concepts s.a. siblings.

How can I prevent Eclipse from supplying deprecated classes when importing?

I have a recurring problem using Eclipse. Consider the following example:
As you can see I've pressed Ctrl+Shift+O. I can choose from a deprecated and a non-deprecated annotation. My problem is that I am often supplied with dozens of classes and half of them are deprecated (a perfect example is the JUnit Assert classes).
My question is how can I make Eclipse ignore all deprecated classes when organizing imports?

Currently Eclipse does not provide such an option... Eclipse Documentation for Organise Imports (Kepler version).
However, with a fudge you can achieve the same result...
Eclipse allows you to provide a list of classes/packages to filter-out.
To do this, navigate to Preferences > Type Filters.
I've done this in my environment to ensure "java.awt.List" is not suggested when I really want "java.util.List".
What you want is to add all deprecated classes to this list.
This list is maintained in your eclipse workspace preferences...
File ... C:\Users\[YOUR_USER_NAME]\workspace\.metadata\.plugins\org.eclipse.core.runtime\.settings\org.eclipse.jdt.ui.prefs
Property ... org.eclipse.jdt.ui.typefilter.enabled=java.awt.List;
All that is required is that you create a list of deprecated classes, and store it in this properties file.
Eclispe can help create this list...
Perform a "Java Search" for "Deprecated".
Then group the results by type.
And copy the results using "Copy Qualified Name"
The results will contain Generics, and this should be removed.
For example, "javafx.scene.control.Cell<T>" should read "javafx.scene.control.Cell".
In addition to containing deprecated classes, the results will also contain any class that has the word "Deprecated". This could be a comment or a method annotation. This list will need to be filtered to retain only deprecated classes.
The script below processes this class list to remove generics, and filtering out classes that are not deprecated (ie, only has method deprecation). The class list is read from a file named "DeprecatedClassList.txt". When it cannot check the class annotation, it skips the class and prints it out (for manual checking).
import java.lang.annotation.Annotation;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class ConfigurationGenerator {
public static void main(String[] args) throws Exception {
List<String> cleanedList = Files
.readAllLines(Paths.get("DeprecatedClassList.txt")).stream()
.map(ConfigurationGenerator::removeGenerics)
.filter(ConfigurationGenerator::hasDeprecatedConstructor)
.collect(Collectors.toList());
String propertyName = "org.eclipse.jdt.ui.typefilter.enabled=";
String propertyValue = String.join(";", cleanedList).concat(";");
String configuration = propertyName + propertyValue;
System.out.println("Configuration property...");
System.out.println(configuration);
}
public static String removeGenerics(String className) {
int openingBracket = className.indexOf("<");
if (openingBracket == -1)
return className;
else
return className.substring(0, openingBracket);
}
public static boolean hasDeprecatedConstructor(String className) {
Class theClass = null;
try {
theClass = Class.forName(className);
} catch (Throwable e) {
// Ignore bad results
System.out.println("Skipping: " + className);
return false;
}
Annotation[] annotations = theClass.getAnnotations();
Optional<Annotation> deprecatedConstructor = Stream
.of(annotations)
.filter(annotation -> annotation.toString().equals(
"#java.lang.Deprecated()")).findAny();
return deprecatedConstructor.isPresent();
}
}
There is one problem with this approach though. You may want to use a deprecated class when a non-deprecated version does not exist. You will not see the deprecated class if it has been purposefully hidden. To resolve that, just be sure you exclude them from the filter.