Description
Using the vlcj component, the custom component appears as a result of the AOP proxy object null.
MediaList Class
public class MediaList {
private libvlc_media_list_t mediaListInstance;
public MediaList(LibVlc libvlc, libvlc_instance_t instance, libvlc_media_list_t mediaListInstance) {
this.libvlc = libvlc;
this.instance = instance;
createInstance(mediaListInstance);
}
private void createInstance(libvlc_media_list_t mediaListInstance) {
logger.debug("createInstance()");
if(mediaListInstance == null) {
mediaListInstance = libvlc.libvlc_media_list_new(instance);
}
else {
libvlc.libvlc_media_list_retain(mediaListInstance);
}
this.mediaListInstance = mediaListInstance; // <- assignment
logger.debug("mediaListInstance={}", mediaListInstance);
mediaListEventManager = libvlc.libvlc_media_list_event_manager(mediaListInstance);
logger.debug("mediaListEventManager={}", mediaListEventManager);
registerEventListener();
}
public final libvlc_media_list_t mediaListInstance() {
return mediaListInstance; // <- proxy object return null, if use aop
}
}
Custom MediaList Class
public class TestMediaList extends MediaList {
public TestMediaList(LibVlc libvlc, libvlc_instance_t instance) {
super(libvlc, instance);
}
public void xTest(String test){
System.out.println(test);
}
}
Spring Configuration Class
#Configuration
public class PlayerBeanConfig {
#Bean
#Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
#Resource
public TestMediaList testMediaList(LibVlc libvlc, libvlc_instance_t instance) {
return new TestMediaList(libvlc, instance);
}
}
AOP Configuration Class
#Aspect
public class MediaListAspect {
#Pointcut("execution(* TestMediaList.xTest(..))")
private void anyMethod() {
}
#Around("anyMethod()")
public Object lockAndUnlock(ProceedingJoinPoint joinPoint) throws Throwable {
Object object = joinPoint.proceed();
return object;
}
}
Test Code
public static void main(String[] args) {
boolean b = new NativeDiscovery().discover();
if (b) {
springContext = new AnnotationConfigApplicationContext(PlayerBeanConfig.class);
String[] kkk = new String[]{};
TestMediaList list = springContext.
getBean(TestMediaList.class, LibVlc.INSTANCE, LibVlc.INSTANCE.libvlc_new(kkk.length, kkk));
System.out.println(list.mediaListInstance()); // <- proxy object return null
} else {
logger.error("Cannot find vlc lib, exit application");
}
}
I try to single step tracking, when TestMediaList the build is complete. MediaListInstance () of the method to return to normal values, but when the spring returns to the proxy object, null is returned. At the same time, I also try to return the value correctly if you don't use AOP.
Therefore, I determine the basic problem in AOP dynamic proxy, but I don't know why, did not previously encountered such a situation.
Minimal example
all class in package : vod.demo
TargetClass
public class TargetClass {
private String returnValue;
public TargetClass() {
this.returnValue = "Hello World";
}
public final String test() {
System.out.println("TargetClass.test();");
return returnValue;
}
}
Aspect Class
#Aspect
public class AspectClass {
#Pointcut("execution(* vod.demo.TargetClass.*(..))")
private void targetMethod() {
}
#Around("targetMethod()")
public Object aroundTarget(ProceedingJoinPoint joinPoint) throws Throwable {
System.out.println("AspectClass.aroundTarget();");
return joinPoint.proceed();
}
}
Spring Config Class
#Configuration
#EnableAspectJAutoProxy
#Import(AspectClass.class)
public class SpringConfig {
#Bean
public TargetClass target() {
return new TargetClass();
}
}
Client Class
public class Client {
public static void main(String[] args) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(SpringConfig.class);
TargetClass target = context.getBean(TargetClass.class);
System.out.println("Client invoke:" + target.test()); // <- output null
}
}
This is a combination of potentially unexpected behaviors. First, Spring uses CGLIB to proxy your beans for AOP. CGLIB proxies are instances of a dynamic subtype of your class that delegate all method calls to a real instance of your class. However, even though the proxy is of a subtype, its fields are not initialized (ie. your TargetClass super constructor is not invoked). A lengthier explanation can be found here.
Additionally, your method
public final libvlc_media_list_t mediaListInstance() {
return mediaListInstance; // <- proxy object return null, if use aop
}
or
public final String test() {
System.out.println("TargetClass.test();");
return returnValue;
}
are final. CGLIB therefore cannot override them to delegate to the real instance. This would be hinted at in Spring logs. For example, you would see
22:35:31.773 [main] INFO o.s.aop.framework.CglibAopProxy - Unable to proxy method [public final java.lang.String com.example.root.TargetClass.test()] because it is final: All calls to this method via a proxy will NOT be routed to the target instance.
Put all of the above together and you get a proxy instance where the field is null and where the proxy cannot delegate to the real instance's method. So your code will actually invoke
public final String test() {
System.out.println("TargetClass.test();");
return returnValue;
}
for an instance where the returnValue field is null.
If you can, change your method, remove the final modifier. If you can't, you'll have to rethink your design.
Related
I am not sure if question is correctly asked because I am still newbie in this stuff.
I want to complete the following scenario using a BeanPostProcessor:
Filter all beans that are marked with #Service annotation.
Filter all methods that have the marker annotation #Refreshable over themselves.
Perform the specified method on the return objects of these methods.
Below is my working example:
#Retention(RUNTIME)
public #interface Refreshable {
}
public interface VisitServiceI {
#Refreshable
VisitDtoOut addVisitToPatient(UUID idPatient, VisitDtoIn visitDtoIn);
}
public interface RefreshableDto {
void copyId();
}
#Component
public class MethodBeanPostProcessor implements BeanPostProcessor {
#Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof VisitServiceI) {
ProxyFactory factory = new ProxyFactory(bean);
factory.addInterface(VisitServiceI.class);
factory.addAdvice((AfterReturningAdvice) (returnValue, method, args, target) -> {
if (method.isAnnotationPresent(Refreshable.class)) {
var refreshableDto = (RefreshableDto) returnValue;
if (refreshableDto != null) {
refreshableDto.copyId();
}
}
});
factory.setExposeProxy(true);
return factory.getProxy();
}
return bean;
}
}
Is this possible to get rid of that useless interfaces like: VisitServiceI
I want to force BeanPostProcessor to somehow works when I will give him standard classes instead of interfaces of them.
Ditch the BeanPostProcessor and just write an aspect instead, let Spring do the heavy lifting.
#Aspect
#Component
public RefreshableAspect {
#AfterReturn("within(#Service) && #annotation(#Refreshable)", returning="retVal")
public void refresh(Object retVal) {
if (retVal instanceof RefreshableDto) {
((RefreshableDto) retVal).copyId();
}
}
}
Something like that will accomplish what you need without interfaces and without an additional BeanPostProcessor.
But if you really want the complex route do something like this
#Component
public class MethodBeanPostProcessor implements BeanPostProcessor {
#Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (AnnotationUtils.findAnnotation(bean.getClass(), Service.class) != null) {
ProxyFactory factory = new ProxyFactory(bean);
factory.setProxyTargetClass(true);
factory.addAdvice((AfterReturningAdvice) (returnValue, method, args, target) -> {
if (method.isAnnotationPresent(Refreshable.class)) {
var refreshableDto = (RefreshableDto) returnValue;
if (refreshableDto != null) {
refreshableDto.copyId();
}
}
});
factory.setExposeProxy(true);
return factory.getProxy();
}
return bean;
}
}
I'm writing a library that uses Spring Security and method security to check whether a user is licensed to perform a certain operation. This is in addition to the usual role-based security, and this is causing a problem.
The annotations look like they do in this test class:
#RestController
class TestController {
#RolesAllowed("ROLE_USER")
#Licensed("a")
public ResponseEntity<String> a() {
return ResponseEntity.ok("a");
}
#RolesAllowed("ROLE_USER")
#Licensed("b")
public ResponseEntity<String> b() {
return ResponseEntity.ok("b");
}
#RolesAllowed("ROLE_USER")
#Licensed("c")
public ResponseEntity<String> c() {
return ResponseEntity.ok("c");
}
}
Having the annotations processed seems simple enough, because you add a customMethodSecurityDataSource:
#EnableGlobalMethodSecurity(
securedEnabled = true,
jsr250Enabled = true,
prePostEnabled = true
)
#Configuration
public class LicenceSecurityConfiguration extends GlobalMethodSecurityConfiguration {
#Override protected MethodSecurityMetadataSource customMethodSecurityMetadataSource() {
return new LicensedAnnotationSecurityMetadataSource();
}
// more configurations
}
But the problem is in Spring's implementation:
#Override
public Collection<ConfigAttribute> getAttributes(Method method, Class<?> targetClass) {
DefaultCacheKey cacheKey = new DefaultCacheKey(method, targetClass);
synchronized (this.attributeCache) {
Collection<ConfigAttribute> cached = this.attributeCache.get(cacheKey);
// Check for canonical value indicating there is no config attribute,
if (cached != null) {
return cached;
}
// No cached value, so query the sources to find a result
Collection<ConfigAttribute> attributes = null;
for (MethodSecurityMetadataSource s : this.methodSecurityMetadataSources) {
attributes = s.getAttributes(method, targetClass);
if (attributes != null && !attributes.isEmpty()) {
break;
}
}
// Put it in the cache.
if (attributes == null || attributes.isEmpty()) {
this.attributeCache.put(cacheKey, NULL_CONFIG_ATTRIBUTE);
return NULL_CONFIG_ATTRIBUTE;
}
this.logger.debug(LogMessage.format("Caching method [%s] with attributes %s", cacheKey, attributes));
this.attributeCache.put(cacheKey, attributes);
return attributes;
}
My custom metadata source is processed first, and as soon as it finds an annotation that it recognises, it stops processing. Specifically, in this if-block:
if (attributes != null && !attributes.isEmpty()) {
break;
}
The result is that my LicenceDecisionVoter votes to abstain; after all, there could be other annotation processors that check roles. And because there are no more attributes to vote upon, only ACCESS_ABSTAIN is returned, and as per Spring's default and recommended configuration, access is denied. The roles are never checked.
Do I have an alternative, other than to implement scanning for Spring's own annotation processors, like the #Secured and JSR-250 annotations?
Or was the mistake to use Spring Security in the first place for this specific purpose?
As promised, the solution. It was more work than I imagined, and the code may have issues because it is partly copied from Spring, and some of that code looks dodgy (or at least, IntelliJ thinks it does).
The key is to remove the GlobalMethodSecurityConfiguration. Leave that to the application itself. The (auto) configuration class looks like the following:
#EnableConfigurationProperties(LicenceProperties.class)
#Configuration
#Import(LicensedMetadataSourceAdvisorRegistrar.class)
public class LicenceAutoConfiguration {
#Bean public <T extends Licence> LicenceChecker<T> licenceChecker(
#Lazy #Autowired final LicenceProperties properties,
#Lazy #Autowired final LicenceFactory<T> factory
) throws InvalidSignatureException, LicenceExpiredException, WrappedApiException,
IOException, ParseException, InvalidKeySpecException {
final LicenceLoader loader = new LicenceLoader(factory.getPublicKey());
final T licence = loader.load(properties.getLicenceFile(), factory.getType());
return factory.getChecker(licence);
}
#Bean MethodSecurityInterceptor licenceSecurityInterceptor(
final LicensedMetadataSource metadataSource,
final LicenceChecker<?> licenceChecker
) {
final MethodSecurityInterceptor interceptor = new MethodSecurityInterceptor();
interceptor.setAccessDecisionManager(decisionManager(licenceChecker));
interceptor.setSecurityMetadataSource(metadataSource);
return interceptor;
}
#Bean LicenceAccessDecisionManager decisionManager(#Autowired final LicenceChecker<?> licenceChecker) {
return new LicenceAccessDecisionManager(licenceChecker);
}
#Bean LicensedMetadataSource licensedMetadataSource() {
return new LicensedMetadataSource();
}
}
The registrar:
public class LicensedMetadataSourceAdvisorRegistrar implements ImportBeanDefinitionRegistrar {
#Override
public void registerBeanDefinitions(final AnnotationMetadata importingClassMetadata,
final BeanDefinitionRegistry registry) {
final BeanDefinitionBuilder advisor = BeanDefinitionBuilder
.rootBeanDefinition(LicensedMetadataSourceAdvisor.class);
advisor.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
advisor.addConstructorArgReference("licensedMetadataSource");
registry.registerBeanDefinition("licensedMetadataSourceAdvisor", advisor.getBeanDefinition());
}
}
And finally, the advisor:
public class LicensedMetadataSourceAdvisor extends AbstractPointcutAdvisor implements BeanFactoryAware {
private final LicenceMetadataSourcePointcut pointcut = new LicenceMetadataSourcePointcut();
private transient LicensedMetadataSource attributeSource;
private transient BeanFactory beanFactory;
private transient MethodInterceptor interceptor;
private transient volatile Object adviceMonitor = new Object();
public LicensedMetadataSourceAdvisor(final LicensedMetadataSource attributeSource) {
this.attributeSource = attributeSource;
}
#Override public void setBeanFactory(final BeanFactory beanFactory) throws BeansException {
this.beanFactory = beanFactory;
}
#Override public Pointcut getPointcut() {
return pointcut;
}
#Override public Advice getAdvice() {
synchronized (this.adviceMonitor) {
if (this.interceptor == null) {
Assert.state(this.beanFactory != null, "BeanFactory must be set to resolve 'adviceBeanName'");
this.interceptor = this.beanFactory.getBean("licenceSecurityInterceptor", MethodInterceptor.class);
}
return this.interceptor;
}
}
class LicenceMetadataSourcePointcut extends StaticMethodMatcherPointcut implements Serializable {
#Override public boolean matches(final Method method, final Class<?> targetClass) {
final LicensedMetadataSource source = LicensedMetadataSourceAdvisor.this.attributeSource;
final Collection<ConfigAttribute> attributes = source.getAttributes(method, targetClass);
return attributes != null && !attributes.isEmpty();
}
}
}
The latter two classes are copied and modified from Spring. The advisor was copied from MethodSecurityMetadataSourceAdvisor, and that's a class that somebody at Spring might have a look at, because of the transient volatile synchronisation object (which I copied, because I can't yet establish if it should be final instead), and because it has a private method that is never used.
I have a flag DISABLE_FLAG and I want to use it to control multiple specific APIs in different controllers.
#RestController
public final class Controller1 {
#RequestMapping(value = "/foo1", method = RequestMethod.POST)
public String foo1()
}
#RestController
public final class Controller2 {
#RequestMapping(value = "/foo2", method = RequestMethod.POST)
public String foo2()
}
I can use an interceptor to handle all the urls. Is there a easy way to do that like annotation?
You could use AOP to do something like that.
Create your own annotation...
#Retention(RetentionPolicy.RUNTIME)
#Target(ElementType.METHOD)
public #interface Maybe { }
and corresponding aspect...
#Aspect
public class MaybeAspect {
#Pointcut("#annotation(com.example.Maybe)")
public void callMeMaybe() {}
#Around("callMeMaybe()")
public Object around(ProceedingJoinPoint joinPoint) throws Throwable {
// do your logic here..
if(DISABLE_FOO) {
// do nothing ? throw exception?
// return null;
throw new IllegalStateException();
} else {
// process the request normally
return joinPoint.proceed();
}
}
}
I don't think there is direct way to disable a constructed request mapping but We can disable API in many ways with some condition.
Here is the 2 ways disabling by spring profile or JVM properties.
public class SampleController {
#Autowired
Environment env;
#RequestMapping(value = "/foo", method = RequestMethod.POST)
public String foo(HttpServletResponse response) {
// Using profile
if (env.acceptsProfiles("staging")) {
response.setStatus(404);
return "";
}
// Using JVM options
if("true".equals(System.getProperty("DISABLE_FOO"))) {
response.setStatus(404);
return "";
}
return "";
}
}
If you are thinking futuristic solution using cloud config is the best approach. https://spring.io/guides/gs/centralized-configuration/
Using Conditional components
This allows to build bean with conditions, if the condition failed on startup, the entire component will never be built. Group all your optional request mapping to new controller and add conditional annotation
#Conditional(ConditionalController.class)
public class SampleController {
#Autowired
Environment env;
#RequestMapping(value = "/foo", method = RequestMethod.POST)
public String foo(HttpServletResponse response) {
return "";
}
public static class ConditionalController implements Condition {
#Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
return context.getEnvironment().acceptsProfiles("staging"); // Or whatever condition
}
}
}
You can solve this with annotations by utilizing spring profiles. You define two profiles one for enabled flag and another profile for the disabled flag. Your example would look like this:
#Profile("DISABLED_FLAG")
#RestController
public final class Controller1 {
#RequestMapping(value = "/foo1", method = RequestMethod.POST)
public String foo1()
}
#Profile("ENABLED_FLAG")
#RestController
public final class Controller2 {
#RequestMapping(value = "/foo2", method = RequestMethod.POST)
public String foo2()
}
Here is the link to the spring framework documentation for this feature: https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/annotation/Profile.html
I did it as follows :
#Retention(RUNTIME)
#Target(ElementType.METHOD)
public #interface DisableApiControl {
}
This class is my customization statement. After could use AOP :
for AbstractBaseServiceImpl :
public abstract class AbstractBaseServiceImpl {
private static boolean disableCheck = false;
public void setDisableChecker(boolean checkParameter) {
disableCheck = checkParameter;
}
public boolean getDisableChecker() {
return disableCheck;
}
}
NOTE : The above class has been prepared to provide a dynamic structure.
#Aspect
#Component
public class DisableApiControlAspect extends AbstractBaseServiceImpl {
#Autowired
private HttpServletResponse httpServletResponse;
#Pointcut(" #annotation(disableMe)")
protected void disabledMethods(DisableApiControl disableMe) {
// comment line
}
#Around("disabledMethods(disableMe)")
public Object dontRun(ProceedingJoinPoint joinPoint, DisableApiControl disableMe) throws Throwable {
if (getDisableChecker()) {
httpServletResponse.sendError(HttpStatus.NOT_FOUND.value(), "Not found");
return null;
} else {
return joinPoint.proceed();
}
}
}
checker parameter added global at this point. The rest will be easier when the value is given as true / false when needed.
#GetMapping("/map")
#DisableApiControl
public List<?> stateMachineFindMap() {
return new ArrayList<>;
}
I have the following classes:
public FooDAO extends AbstractDAO<Foo> { // Dropwizard DAO
#Inject FooDAO(SessionFactory sf) { super(sf); }
public void foo() { /* use SessionFactory */ }
}
public class FooService {
private final FooDAO fooDAO; // Constructor-injected dependency
#Inject FooService (FooDAO fooDAO) { this.fooDAO = fooDAO; }
#UnitOfWork
public void foo() {
this.fooDAO.foo();
System.out.println("I went through FooService.foo()");
}
}
Now, FooService is not a resource, so Dropwizard doesn't know about it and doesn't automagically proxy it. However the smart guys at Dropwizard made it so I can get a proxy through UnitOfWorkAwareProxyFactory.
I tried doing feeding these proxies to Guice with an interceptor, but I faced an issue because UnitOfWorkAwareProxyFactory only ever creates new instances and never lets me pass existing objects. The thing with new instances is that I don't know the parameters to give it since they're injected by Guice.
How do I create #UnitOfWork-aware proxies of existing objects?
Here's the interceptor I've made so far:
public class UnitOfWorkModule extends AbstractModule {
#Override protected void configure() {
UnitOfWorkInterceptor interceptor = new UnitOfWorkInterceptor();
bindInterceptor(Matchers.any(), Matchers.annotatedWith(UnitOfWork.class), interceptor);
requestInjection(interceptor);
}
private static class UnitOfWorkInterceptor implements MethodInterceptor {
#Inject UnitOfWorkAwareProxyFactory proxyFactory;
Map<Object, Object> proxies = new IdentityHashMap<>();
#Override public Object invoke(MethodInvocation mi) throws Throwable {
Object target = proxies.computeIfAbsent(mi.getThis(), x -> createProxy(mi));
Method method = mi.getMethod();
Object[] arguments = mi.getArguments();
return method.invoke(target, arguments);
}
Object createProxy(MethodInvocation mi) {
// here, what to do? proxyFactory will only provide objects where I pass constructor arguments, but... I don't have those!
}
}
}
Of course, if Dropwizard (or Guice) offers me a simpler way to do so, which is it?
As from Dropwizard 1.1: (not yet released, as of August 10, 2016)
public class UnitOfWorkModule extends AbstractModule {
#Override
protected void configure() {
UnitOfWorkInterceptor interceptor = new UnitOfWorkInterceptor();
bindInterceptor(Matchers.any(), Matchers.annotatedWith(UnitOfWork.class), interceptor);
requestInjection(interceptor);
}
#Provides
#Singleton
UnitOfWorkAwareProxyFactory provideUnitOfWorkAwareProxyFactory(HibernateBundle<AlexandriaConfiguration> hibernateBundle) {
return new UnitOfWorkAwareProxyFactory(hibernateBundle);
}
private static class UnitOfWorkInterceptor implements MethodInterceptor {
#Inject
UnitOfWorkAwareProxyFactory proxyFactory;
#Override
public Object invoke(MethodInvocation mi) throws Throwable {
UnitOfWorkAspect aspect = proxyFactory.newAspect();
try {
aspect.beforeStart(mi.getMethod().getAnnotation(UnitOfWork.class));
Object result = mi.proceed();
aspect.afterEnd();
return result;
} catch (InvocationTargetException e) {
aspect.onError();
throw e.getCause();
} catch (Exception e) {
aspect.onError();
throw e;
} finally {
aspect.onFinish();
}
}
}
}
Hi I request your help to know how to emulate the method of the class Validator.validateConnection();.
The problem is that the method validateConnection not exist in the class Class_Implementation and I don't want to create that method in the class Class_Implementation. The method validateConnection do a connection to the database to know if the connection is alive. When Mockito runs I get a java.Lang.NullPointerException that is caused by NamingException - need to specify class name in environment.
The real problem is when I call in Mockito test the line:
Boolean resp = mockImpl.checkConnection();
..in the checkConnection() the class Validator.validateConnection(); is trying to connect to database. I just want emulate this line and return true or false, but the problem is that the method validateConnection() is an instance of class Validator.
If need more information for fix this please let me know.
public class Class_Implementation {
public boolean checkConnection() {
boolean isConnectionAlive = false;
Validator.validateConnection();
// another things for do
return false;
}
}
public class Validator {
public static Boolean validateConnection() {
Connection conn = new Connection();
Boolean connectionAlive = false;
connectionAlive = conn.isConnectionAlive();
if (connectionAlive) {
return true;
} else {
return false;
}
}
}
public class Connection {
public boolean isConnectionAlive() {
// Code for connection to DB
}
}
// class for do the test
#RunWith(PowerMockRunner.class)
#PrepareForTest({Class_Implementation.class,Validator.class})
public class TestConnection {
#Test
public void validate_Connection() throws Exception {
Class_Implementation mockImpl = PowerMock.createPartialMock(Class_Implementation.class);
PowerMock.mockStatic(Validator.class);
PowerMockito.when(mockImpl, Validator.validateConnection() ).thenReturn(true);
PowerMock.replayAll(mockImpl);
Boolean resp = mockImpl.checkConnection();
PowerMock.verifyAll();
Validate.notNull(resp);
}
}
Use a Validator object instead of its static methods and inject the Validator into Class_Implementation (by constructor). This is called Dependency Injection. In your test you can inject a mock of the Validator.
public class Validator {
public boolean validateConnection() {
...
}
}
public class Class_Implementation {
private final Validator validator;
public Class_Implementation(Validator validator) {
this.validator = validator;
}
public boolean checkConnection() {
...
validator.validateConnection();
...
}
}
public public class Class_ImplementationTest {
#Test
public void validate_Connection() throws Exception {
Validator validator = Mockito.mock(Validator.class);
Mockito.when(validator.validateConnection()).thenReturn(true);
Class_Implementation impl = new Class_Implementation(validator);
boolean response = mockImpl.checkConnection();
Assert.assertTrue(response);
}
}
I made some additional changes to your code.
Don't return a Boolean object if there are only two states.
A Unit test tests on class and is named like the class with an additional Test prefix.
You don't need PowerMock if you have nice code.
Just mock your Class_Implementation (you should change the name and stick to Java naming standards by the way) and stub the validateConnection() method:
final Class_Implementation mock = mock(Class_Implementation.class);
when(mock.checkConnection()).thenReturn(true); // or false
But anyway, what you should mock is the interface to start with.