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Avoiding code duplication when checking for default responses

I have a Java program that calls an external API (RealApi in the code below) and sometimes I want to avoid calling this API and instead return pre-constructed responses (generated by FakeApi).
So, I ended up duplicating this kind of construct in most of my methods:
public Type1 m1(String s) {
try {
Type1 r = FakeApi.m1(s);
if (r != null) {
return r;
}
} catch (Exception e) {
// log error
}
return RealApi.m1(s);
}
What are some options to avoid duplicating this try/catch block everywhere? It's important that if FakeApi throws an exception or returns null, the RealApi must be called.

One option would be encapsulate the error checking behaviour into its own method:
public <T> T fakeOrReal(Supplier<T> fake, Supplier<T> real) {
try {
T r = fake.get();
if (r != null) {
return r;
}
}
catch (Exception e) {
// log error
}
return real.get();
}
You can then just call it with
public Type1 m1(String s) {
return fakeOrReal(() -> FakeApi.m1(s), () -> RealApi.m1(s));
}

This is not as simple as Thomas Preißler's answer but it will help you not repeat any method at all. So if you expand the interface, you have to modify only the concrete classes and not the linker which describes the actual behavior you want.
Create an interface that contains all the methods of RealApi:
interface Api {
Type1 m1(String s);
}
Then a class that does the actual call:
class ConcreteApi implements Api {
public Type1 m1(String s) {
return RealApi.m1(s);
}
}
Then create your FakeApi:
class TotallyFakeApi implements Api {
public Type1 m1(String s) {
return FakeApi.m1(s);
}
}
Now, the tricky part to avoid repeating yourself:
private static Object callImplementation(Api api, Method method, Object[] methodArgs) throws Exception {
Method actualMethod = api.getClass().getMethod(actualMethod.getName(), actualMethod.getParameterTypes());
return actualMethod.invoke(api, methodArgs);
}
Api fakeOrReal(Api fakeApi, Api realApi) {
return (Api) Proxy.newProxyInstance(
FakeApi.class.getClassLoader(),
new Class[]{Api.class},
(proxy, method, methodArgs) -> {
try {
Object r = callImplementation(fakeApi, method, methodArgs);
if (r != null) {
return r;
}
} catch (Exception e) {
// logError(e);
}
return callImplementation(realApi, method, methodArgs);
}
);
}
Get the actual implementation like this:
Api apiToUse = fakeOrReal(new TotallyFakeApi(), new ConcreteApi());

java Mockito verify abstract method

i have an issue on verifying a call to method of class under test, using the verify() method it tells that the call is not done to that method, this method is defined as abstract in super class (loadFile(String))
find bellow the code :
public abstract class FileParser {
public Iterator<String> loadFile(FileSettingsToSend fileSetting) {
System.out.println("file before staged");
try {
if(!movFile("staged",fileSetting))
return null;
System.out.println("file after move "+fileSetting.getFile().getAbsolutePath());
boolean isValidFormatFile = fileValidator.checkFileFormat(fileSetting);
if (!isValidFormatFile) {
System.out.println("file format is not valid");
return null;
}
return readBlock(fileSetting);
} catch (Exception e) {
System.out.println(e.getMessage());
return null;
} finally {
}
//return null;
}
public abstract Iterator<String> readBlock(FileSettingsToSend fileSettingsToSend)
throws JsonProcessingException, IOException;
}
public class JsonFileParser extends FileParser {
public final ObjectMapper mapper = new ObjectMapper();
#Autowired
public JsonFileParser(FileValidator jsonFileValidatorService, FileAttributeService fileAttributeService) {
super(jsonFileValidatorService, fileAttributeService);
}
#Override
public Iterator<String> readBlock(FileSettingsToSend fileSetting) throws JsonProcessingException, IOException {
ObjectMapper mapper = new ObjectMapper();
System.out.println("inside readBlock json implementation");
List<String> listAttribute = fileAttributeService.getAttributes(fileSetting.getDiretoryPath());
String[] blocDelimitor = fileAttributeService.getDelimitorRepositpry(fileSetting.getDiretoryPath());
System.out.println("after validator");
final JsonNode root = mapper.readTree(fileSetting.getFile());
if (root == null)
return null;
Iterator<JsonNode> nodeIterator = root.elements();
System.out.println("Data is " + root);
return new Iterator<String>() {
JsonNode node;
#Override
public boolean hasNext() {
return nodeIterator.hasNext();
}
#Override
public String next() {
int i = 0;
node = nodeIterator.next();
System.out.println("after nex " + node.toString());
Arrays.stream(blocDelimitor).forEach(e -> {
node = node.path(e);
System.out.println("inside next " + node.toString());
});
String result = null;
if (node.isArray()) {
System.out.println("It is Array");
for (JsonNode node1 : node) {
if (i != 0)
result = result + "," + listAttribute.stream().map(e -> e + "=" + node1.get(e))
.collect(Collectors.joining(","));
else
result = listAttribute.stream().map(e -> e + "=" + node1.get(e))
.collect(Collectors.joining(","));
i++;
}
} else
result = listAttribute.stream().map(e -> e + "=" + node.get(e)).collect(Collectors.joining(","));
return result;
}
};
}
Test method is :
#Mock
FileValidator jsonFileValidatorService;
#Mock
FileAttributeService fileAttributeService;
JsonFileParser jsonFileParserMock = new JsonFileParser(jsonFileValidatorService, fileAttributeService);
#Test
public void validatorNotTrue() throws JsonProcessingException, IOException{
when(jsonFileValidatorService.checkFileFormat( anyObject() )).thenReturn(true);
JsonFileParser jsonFileParser = Mockito.spy(jsonFileParserMock);
doReturn(true).when(jsonFileParser).movFile(anyString(),anyObject() );
assertNull(jsonFileParser.loadFile(null));
verify(jsonFileParser, times(1)).movFile(anyString(),anyObject());
assertTrue(jsonFileParser.movFile(anyString(), anyObject()));
assertTrue(jsonFileValidatorService.checkFileFormat( anyObject() ));
//exception.expect(Exception.class);
verify(jsonFileParser,times(1)).readBlock(anyObject();
}
#BeforeClass
public static void settingUp(){
}
#Before
public void initMock(){
MockitoAnnotations.initMocks(this);
}
the line verify(jsonFileParser,times(1)).readBlock(anyObject(); return false; meaning that the method loadFile of jsonfileParser not called
can you get your held to tell why it is not called.
Thank you.

This happens because you initialize the mocks after you create a JsonFileParser. Note that #Before method is executed after all the fields of your test class are initialized.
As a result, you pass null dependencies to the class. The invocation to the null FileValidator throws NullPointerException, but you swallow it in your catch block.
Generally it is advisable to verify the arguments you pass to your constructors and methods, to fail fast in case of an error. For example, Java comes with a handy Objects::requireNonNull method to verify that the passed parameters are non-null.
Similarly it's generally a bad practice to swallow every single exception. For instance, in your example, you expect IOException and JsonProcessingException to be thrown. It's better to catch these explicitly and let the program crash (or at least log a warning) for any other one.
Finally, mocks and spies are prone to overuse. Usually, it's enough to use fakes - dummy implementations of your interfaces. Depending on how much control you have over the code, you may also want to refactor it to avoid using a spy at all. Using one in a code you may freely change may signal an architectural problem.

How do I dynamically create a common proxy class of two unrelated classes?

I have two unrelated java classes (only *.class, no *.java) like this:
public class Trick {
public String getName() { return "Jack"; }
public String trick() { ... }
}
and
public class Treat {
public String getName() { return "John"; }
public String treat() { ... }
}
and I would like to generate a sort of Proxy class at runtime that represents the union of both classes and forwards them to the respective instance, and maybe throw if that's not possible. I assume that can be done with cglib but I don't know where to start.
This is what I would like to do (pseudocode):
// prepare: generate a common interface
TrickOrTreat trickOrTreat = magic.createUnionInterface(Trick.class, Treat.class);
// use with concrete interface A:
Trick trick = new Trick();
TrickOrTreat proxyA = magic.createProxy(trickOrTreat.class, trick);
System.out.println("trick name: " + proxyA.getName());
// use with concrete interface B:
Treat treat = new Treat();
TrickOrTreat proxyB = magic.createProxy(trickOrTreat.class, treat);
System.out.println("treat name: " + proxyB.getName());
Or something to that effect. I would like to do it completely dynamically, probably cglib-based? If thats not possible I would do it with a code generation step in between?

If you are willing to trade in cglib, you can do this with Byte Buddy. I typically refuse to call it magic but here you go:
class Magic {
Class<?> createUnionInterface(Class<?> a, Class<?> b) {
DynamicType.Builder<?> builder = new ByteBuddy().makeInterface();
Set<MethodDescription.SignatureToken> tokens = new HashSet<>();
for (MethodDescription m : new TypeDescription.ForLoadedType(a)
.getDeclaredMethods()
.filter(ElementMatchers.isVirtual())) {
tokens.add(m.asSignatureToken());
builder = builder.defineMethod(m.getName(),
m.getReturnType(),
m.getModifiers()).withoutCode();
}
for (MethodDescription m : new TypeDescription.ForLoadedType(b)
.getDeclaredMethods()
.filter(ElementMatchers.isVirtual())) {
if (!tokens.contains(m.asSignatureToken())) {
builder = builder.defineMethod(m.getName(),
m.getReturnType(),
m.getModifiers()).withoutCode();
}
}
return builder.make()
.load(Magic.class.getClassLoader())
.getLoaded();
}
Object createProxy(Class<?> m, final Object delegate) throws Exception {
return new ByteBuddy()
.subclass(m)
.method(new ElementMatcher<MethodDescription>() {
#Override
public boolean matches(MethodDescription target) {
for (Method method : delegate.getClass()
.getDeclaredMethods()) {
if (new MethodDescription.ForLoadedMethod(method)
.asSignatureToken()
.equals(target.asSignatureToken())) {
return true;
}
}
return false;
}
}).intercept(MethodDelegation.to(delegate))
.make()
.load(Magic.class.getClassLoader())
.getLoaded()
.newInstance();
}
}
Note that you cannot reference a runtime-generated type at compile-time. This is however a given constraint with runtime code generation.
Magic magic = new Magic();
Class<?> trickOrTreat = magic.createUnionInterface(Trick.class, Treat.class);
Trick trick = new Trick();
Object proxyA = magic.createProxy(trickOrTreat, trick);
System.out.println("trick name: " + trickOrTreat.getDeclaredMethod("getName").invoke(proxyA));
Treat treat = new Treat();
Object proxyB = magic.createProxy(trickOrTreat, treat);
System.out.println("trick name: " + trickOrTreat.getDeclaredMethod("getName").invoke(proxyB));
You can overcome this by generating your TrickOrTreat class prior to runtime such that you can reference the type at runtime.
As for the suggested union-type approach, this would require you to have at least one class to be an interface type as Java does not support multiple inheritance.

If you need functionality of both classes/interfaces you can use
public <TT extends Trick & Treat> void process(TT thing){
//...
}
edit:
Implement new Interface MyProxyHandler
public interface MyProxyHandler {}
Extend it with interfaces of classes say TreatInterface and TrickInterface
Create class ProxyManager that implements java.lang.reflect.InvocationHandler
public abstract class ProxyManager<T extends MyProxyHandler> implements InvocationHandler {
protected static String LOCK_OBJECT = new String("LOCK");
protected T proxyHandler;
protected List<T> handlers = new ArrayList<>();
#SuppressWarnings("unchecked")
public ProxyManager(Class<T> _clazz) {
proxyHandler = (T) Proxy.newProxyInstance(_clazz.getClassLoader(), new Class[]{_clazz}, this);
}
public T getProxy() {
return proxyHandler;
}
public List<T> getHandlers() {
return handlers;
}
public void setHandlers(List<T> handlers) {
this.handlers = handlers;
}
public boolean registerHandler(T handler) {
synchronized (LOCK_OBJECT) {
boolean add = true;
for (T item : this.handlers) {
if (item.getClass().equals(handler.getClass())) {
add = false;
}
}
if (add)
this.handlers.add(handler);
return add;
}
}
#Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String result = "";
for (MyProxyHandler handler : getHandlers()) {
try {
//I recommend that methods returns some enum like HANDLED/NOTHANDLED
result = (String) method.invoke(handler, args);
if (result.equals("Some flag"))
break;
} catch (InvocationTargetException e) {
throw e.getCause();
}
}
return result;
}
}
Extend that class with your concrete class
public class TreatTrickProxyManager<T extends TreatInterface & TreatInterface> extends ProxyManager<T> {
public TreatTrickProxyManager(Class<T> _clazz) {
super(_clazz);
}
}
In your bussines logic class get an instance of TreatTrickProxyManager
In your method
public void retrieveSomeData(){
((TreatTrickProxyManager)getTreatTrickProxyManager().getProxy()).someMethodInvocation()
}

Getting method regardless of parameters

I am trying to get method regardless of what parameters that method takes (as of now there is no method overloading and there wouldn't be in future). The only possible solution that i could come up with was
private Method getMethod(Class<?> clas, String methodName) {
try {
Method[] methods = clas.getMethods();
for (Method method : methods) {
if (method.getName().equalsIgnoreCase(methodName)) {
return method;
}
}
} catch (SecurityException e) {
e.printStackTrace();
}
return null;
}
What i want to ask that is there a way to fetch a method regardless of its parameters ? I was looking at clas.getMethod ("methodName", parameters) and if i provide null in there it will try to fetch a method which has no parameters. Which wouldn't be no case.
Any ideas ?
EDIT
Thanks guys for input. In my case, i know that there would be only one method regardless of its case. The reason i am using ignoreCase is because the input will be coming from a developer (in other team) and he will be providing the name as a hard-coded string. So to keep things from spilling out of our hands, I am using a safe approach.

No. The way you've done it is the way to go. A method is identified by its signature and the signature includes the name and the parameter types.

Here is a solution that retrieves all methods with the specified class and method name regardless of the method's parameters:
public class Test
{
private class Foo
{
public void bar()
{
}
public void bar(String s)
{
}
public void goo()
{
}
}
private static Method[] getMethods(Class<?> clazz, String methodName)
{
List<Method> methods = new ArrayList<Method>();
Method[] declaredMethods = clazz.getDeclaredMethods();
for (Method declaredMethod: declaredMethods)
{
if (declaredMethod.getName().equals(methodName))
{
methods.add(declaredMethod);
}
}
return methods.toArray(new Method[methods.size()]);
}
public static void main(String[] args)
{
Method[] methods = getMethods(Foo.class, "bar");
System.out.println(Arrays.toString(methods));
}
}
This generates the following output:
[public void com.example.Test$Foo.bar(java.lang.String), public void com.example.Test$Foo.bar()]

You've done just fine. This is basically the same as the solution to a similar problem I dealt with four years ago, creating a means to create callback methods in Java. The constructors for my Callback class were:
public Callback(Class<?> clazz, String methodName, Object parentObj) {
// Find a method with the matching name
Method[] allMethods;
try { allMethods = clazz.getMethods(); }
catch(SecurityException se) { allMethods = new Method[0]; }
int count = 0;
Method single = null;
for(Method m : allMethods) {
if(m.getName().equals(methodName)) {
single = m;
count++;
}
// Can't have more than one instance
if(count > 1)
throw new IllegalArgumentException(clazz.getName()
+ " has more than one method named " + methodName);
}
if(count == 0) // No instances found
throw new IllegalArgumentException(clazz.getName()
+ " has no method named " + methodName);
this.parentObj = parentObj;
this.method = single;
this.parameters = single.getParameterTypes();
}
public Callback(
Class<?> clazz,
String methodName,
Object parentObj,
Class<?>...parameters)
{
try { this.method = clazz.getMethod(methodName, parameters); }
catch(NoSuchMethodException nsme) { nsme.printStackTrace(); }
catch(SecurityException se) { se.printStackTrace(); }
this.parentObj = parentObj;
this.parameters = parameters;
}
My Callback class isn't really useful any more in the era of Java 8, but at the time the only real means for a "callback" in java was anonymous interface implementations, which wasn't sufficient for my use-case.
As you can see in the first constructor, it throws an exception if it finds multiple methods with the same name.

Using java streams there is a really short method of finding a method, the first match, by its name only:
Stream.of(type.getMethods())
.filter((m) -> m.getName().equals(searchedName))
.findFirst()
.get();
I think this is a short and readable possibility in this case.

Base Method Invocation on enum

I'm learning about Java enums and I was wondering what is the best approach to check multiple enums for a matching value in order to call a specific method. I have defined two separate enums below that are used by getValue method's colName parameter to determine what method to execute. So the enum drives the method call. There has to be a more efficient way to do this than what I have below. Any suggestions?
I want to avoid having to do the below (pseudo code):
if(colName.equalsIgnoreCase("ATTRIBUTEONE") ||
colName.equalsIgnoreCase("ATTRIBUTETWO") ||
colName.equalsIgnoreCase("ATTRIBUTETWO")){
callAsStringMethod();
} else if(colName.equalsIgnoreCase("ATTRIBUTEFOUR")){
callAsIntegerMethod();
}
My Attempt using enum:
public class RowHelper implements IRowHelper
public static enum StringAttributes {
ATTRIBUTEONE,
ATTRIBUTETWO,
ATTRIBUTETHREE;
}
public static enum IntegerAttributes {
ATTRIBUTEFOUR,
ATTRIBUTEFIVE,
ATTRIBUTESIX,
ATTRIBUTESEVEN;
}
#Override
public String getValue(String colName) throws Exception{
boolean colFound=false;
Object retValue = null;
for (EConstants.StringAttributes attribute : EConstants.StringAttributes.values()) {
if(colName.toUpperCase().equals(attribute)){
retValue = callAsStringMethod();
colFound=true;
}
}
for (EConstants.IntegerAttributes attribute : EConstants.IntegerAttributes.values()) {
if(colName.toUpperCase().equals(attribute)){
retValue = callAsIntegerMethod();
colFound=true;
}
}
if(!colFound)
throw new Exception("column not found");
if(retValue instanceof String )
return (String) retValue;
else
return retValue.toString();
}
}

Try this:
public String getValue(String colName) throws Exception {
final String name = colName != null ? colName.trim().toUpperCase() : "";
try {
EConstants.StringAttributes.valueOf(name);
return callAsStringMethod().toString();
} catch (Exception e1) {
try {
EConstants.IntegerAttributes.valueOf(name);
return callAsIntegerMethod().toString();
} catch (Exception e2) {
throw new Exception("column not found");
}
}
}
The method's now returning the appropriate value, according to the latest edit of the question.
EDIT :
According to Kirk Woll and Louis Wasserman's benchmark, looping through values is significantly faster than doing a try/catch. So here's a simplified version of the original code, expect it to be a bit faster:
public String getValue(String colName) throws Exception {
final String name = colName != null ? colName.trim().toUpperCase() : "";
for (EConstants.StringAttributes attribute : EConstants.StringAttributes.values())
if (name.equals(attribute))
return callAsStringMethod().toString();
for (EConstants.IntegerAttributes attribute : EConstants.IntegerAttributes.values())
if (name.equals(attribute))
return callAsIntegerMethod().toString();
throw new Exception("column not found");
}

Well, this is a weird design ._. Anyway, you can use enum, but I would something like:
public interface RowAttribute {
String getValue(IRowHelper rowHelper);
}
public class StringRowAttribute implements RowAttribute {
#Override
public String getValue(IRowHelper rowHelper) {
return rowHelper.callAsStringMethod();
}
}
public class IntegerRowAttribute implements RowAttribute {
#Override
public String getValue(IRowHelper rowHelper) {
return rowHelper.callAsIntegerMethod().toString();
}
}
public class RowHelper implements IRowHelper {
private static final RowAttribute INTEGER_ATTRIBUTE = new IntegerRowAttribute();
private static final RowAttribute STRING_ATTRIBUTE = new StringRowAttribute();
private static enum Attribute {
ATTRIBUTEONE(INTEGER_ATTRIBUTE),
ATTRIBUTETWO(INTEGER_ATTRIBUTE),
ATTRIBUTETHREE(INTEGER_ATTRIBUTE);
ATTRIBUTEFOUR(STRING_ATTRIBUTE),
ATTRIBUTEFIVE(STRING_ATTRIBUTE),
ATTRIBUTESIX(STRING_ATTRIBUTE),
ATTRIBUTESEVEN(STRING_ATTRIBUTE);
private final RowAttribute attribute;
private Attribute(RowAttribute attribute) {
this.attribute = attribute;
}
public RowAttribute getAttributeResolver() {
return this.attribute;
}
}
#Override
public String getValue(String colName) throws Exception {
final String name = colName != null ? colName.trim() : "";
for (Attribute attribute : Attribute.values()) {
if (attribute.name().equalsIgnoreCase(name)) {
return attribute.getAttributeResolver().getValue(this);
}
}
throw new Exception(String.format("Attribute for column %s not found", colName));
}
}
Then you don't need to create more than one enum and use its power to iterate through the possible values. You would only need to make the methods callAsStringMethod/callAsIntegerMethod public. Another way is to insert the implementations inside RowHelper. Something like this:
public class RowHelper implements IRowHelper {
public interface RowAttribute {
String getValue();
}
private static final RowAttribute INTEGER_ATTRIBUTE = new RowAttribute() {
#Override
public String getValue() {
return callAsIntegerMethod().toString();
}
};
private static final RowAttribute STRING_ATTRIBUTE = new RowAttribute() {
#Override
public String getValue() {
return callAsStringMethod();
}
};
...
#Override
public String getValue(String colName) throws Exception {
...
if (attribute.name().equalsIgnoreCase(name)) {
return attribute.getAttributeResolver().getValue();
}
...
}
}
Anyway, I don't understand in your method how you get the attribute value really without passing as parameter the colName to it.

The most efficient way to do this with multiple enums is, frankly, to make them the same enum. There isn't really a better way.
That said, instead of the loop you have, you can use Enum.valueOf(EnumClass.class, name) to find the enum value of that type with the specified name, rather than looping like you're doing.