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Better way to continue after exceptions in java

Assuming I have to read from a file, and then construct a java object out of it.
PersonData p = new PersonData();
p.setName(readTokenAsString());
p.setAge(AgeConverter.createFromDateOfBirth(readTokenAsString())); // this throws a checked exception if the date of birth is mal-formed.
//... a list of methods that throws exception as AgeConverter
Behavior I want: If one attribute has problem, just ignore it and keep process other attributes.
Solution I can think of:
try {
p.setAge1(...);
} catch (Exception e) {
//log and ignore
}
try {
p.setAge2(...);
} catch (Exception e) {
//log and ignore
}
//repeat for each attribute
Question:
Is there better way to do this to avoid repetition? Functional style maybe?
a) What's the best approach if I cannot modify PersonData class.
b) What's the best approach if I can rewrite PersonData class.

Given your current declaration, I would do it as follows.
Define a #FunctionalInterface to which you can pass your I/O logic:
#FunctionalInterface
public interface CheckedSupplier<T> {
T getValue() throws Exception;
}
Define an utility method that consumes the #FunctionaInterface:
public static final <T> T getValueWithDefault(CheckedSupplier<T> supplier, T defaultValue) {
try {
return supplier.getValue();
} catch (Exception e){
return defaultValue;
}
}
Use the utility method as follows:
PersonData p = new PersonData();
p.setName(getValueWithDefault(() -> readTokenAsString(), "default"));
p.setAge(getValueWithDefault(() -> AgeConverter.createFromDateOfBirth(readTokenAsString()), 0));
This should do the trick regardless of weather you want modify the PersonData class or not.

If you use Java 8 you can do something like this. Create your own functional interface with one method that throws Exception
public interface MyConsumer<T> {
public void process(T t) throws Exception;
}
And create a static method to use that interface
public static <T> void setAndLogException(T value, MyConsumer<T> consumer) {
try {
consumer.process(value);
} catch (Exception e) {
// log exception
}
}
And then using it like setAndLogException(AgeConverter.createFromDateOfBirth(readTokenAsString()), p::setAge);

You can also use solution provided by this: https://stackoverflow.com/a/28659553/6648303
This solution won't complain at compile phase about checked Exceptions.
It would be something like this:
public static void ignoringExc(RunnableExc r) {
try { r.run(); } catch (Exception e) { }
}
#FunctionalInterface public interface RunnableExc { void run() throws Exception; }
and then:
PersonData p = new PersonData();
ignoringExc(() -> p.setName(readTokenAsString()));
...

How to reduce code duplication when using non-compatible wrappers

[TL;DR]
The problem is, in AWrapper and AType I have to duplicate pretty much whole function, where there is always the syntax:
public [TYPE/void] METHOD([OPT: args]) throws TestFailedException {
[OPT: TYPE result = null;]
long startTime = System.currentTimeMillis();
while (true) {
try {
beforeOperation();
[OPT: result =] ((WrappedType) element).METHOD([OPT: args]);
handleSuccess();
break;
} catch (Exception e) {
handleSoftFailure(e);
if (System.currentTimeMillis() - startTime > TIMEOUT) {
handleFailure(e);
break;
} else {
try {
Thread.sleep(WAIT_FOR_NEXT_TRY);
} catch (InterruptedException ex) {
}
}
}
}
[OPT: return result;]
}
Lets say I have 2 classes I don't own:
public class IDontOwnThisType {
public void doA(String string) { System.out.println("doA"); }
public String doB(); {System.out.println("doB"); return "doB";}
public OtherTypeIDoNotOwn doC() {System.out.println("doC"); return new OtherTypeIDoNotOwn();}
}
public OtherTypeIDoNotOwn {
public void doD() { System.out.println("doD"); }
public String doE() { System.out.println("doE); }
public OtherTypeIDoNotOwn doF(String string) {System.out.println("doF"); return new OtherTypeIDoNotOwn();}
}
So, I have an interface:
public interface OperationManipulator {
void beforeOperation(); //called before operation
void handleSuccess(); //called after success
void handleSoftFailure(Exception e); //called after every failure in every try
void handleFailure(Exception e) throws TestFailedException; //called after reaching time limit
}
Then interface that extends above one, "mimicking" methods of external classes, but throwing custom exception:
public interface IWrapper<T extends IType> extends OperationManipulator {
public void doA(String string) throws TestFailedException;
public String doB() throws TestFailedException;
public T doC() throws TestFailedException;
}
Then we have IType, which also extends OperationManipulator:
public interface IType<T extends IType> extends OperationManipulator {
public void doD() throws TestFailedException;
public String doE() throws TestFailedException;
public T doF(String string) throws TestFailedException;
}
Then, we have abstract implementations of above interfaces:
public abstract class AType<T extends IType> implements IType{
Object element; // I do not own type of this object, cant modify it.
Class typeClass;
long TIMEOUT = 5000;
long WAIT_FOR_NEXT_TRY = 100;
public AType(Object element) {
this.element = element;
elementClass = this.getClass();
}
/* ... */
}
Then, we override functions from the interfaces, excluding OperationManipulator interface:
Function not returning anything version:
#Override
public void doD() throws TestFailedException {
long startTime = System.currentTimeMillis();
while (true) {
try {
beforeOperation();
((OtherTypeIDoNotOwn) element).doD();
handleSuccess();
break;
} catch (Exception e) {
handleSoftFailure(e);
if (System.currentTimeMillis() - startTime > TIMEOUT) {
handleFailure(e);
break;
} else {
try {
Thread.sleep(WAIT_FOR_NEXT_TRY);
} catch (InterruptedException ex) {
}
}
}
}
Function returning normal reference version:
#Override
public String doE() throws TestFailedException {
String result = null;
long startTime = System.currentTimeMillis();
while (true) {
try {
beforeOperation();
result = ((OtherTypeIDoNotOwn) element).doE();
handleSuccess();
break;
} catch (Exception e) {
handleSoftFailure(e);
if (System.currentTimeMillis() - startTime > TIMEOUT) {
handleFailure(e);
break;
} else {
try {
Thread.sleep(WAIT_FOR_NEXT_TRY);
} catch (InterruptedException ex) {
}
}
}
}
return result;
}
And function returning object of type parameter:
#Override
public T doF(String string) throws TestFailedException {
T result = null;
long startTime = System.currentTimeMillis();
while (true) {
try {
beforeOperation();
OtherTypeIDoNotOwn temp = ((OtherTypeIDoNotOwn) element).doF(string);
result = (T) elementClass.getDeclaredConstructor(Object.class).newInstance(temp);
handleSuccess();
break;
} catch (Exception e) {
handleSoftFailure(e);
if (System.currentTimeMillis() - startTime > TIMEOUT) {
handleFailure(e);
break;
} else {
try {
Thread.sleep(WAIT_FOR_NEXT_TRY);
} catch (InterruptedException ex) {
}
}
}
}
return result;
}
The same goes for AWrapper, but the differences are:
constructor have class argument of stored type
object is cast to IDoNotOwnThisType instead of OtherTypeIDoNotOwn. Functions of this object also may return OtherTypeIDoNotOwn.
IDoNotOwnThisType is type that AWrapper is wrapping.
OtherTypeIDoNotOwn is type that AType is wrapping.
Then, we have implementation of these abstract classes:
public class AssertingType extends AType<AssertingType> {
public AssertingType(Object element) {
super(element);
}
#Override
public void beforeOperation() {
//System.out.println("Asserting type before operation!");
}
#Override
public void handleSuccess() {
//TODO: add to log file and log to output
System.out.println("Asserting type success!");
}
#Override
public void handleFailure(Exception e) throws TestFailedException {
//TODO: add to log file, log to output and throw exception
System.out.println("Asserting type failure!");
e.printStackTrace();
throw new TestFailedException();
}
#Override
public void handleSoftFailure(Exception e) {
//TODO: add to log file, log to output
System.out.println("Asserting type soft failure!");
e.printStackTrace();
}
}
And:
public class AssertingWrapper extends AWrapper<AssertingType> {
public AssertingWrapper (Object driver) {
super(driver, AssertingType.class);
}
#Override
public void beforeOperation() {
//TODO
System.out.println("Asserting wrapper success!");
}
#Override
public void handleSuccess() {
//TODO: add to log file and log to output
System.out.println("Asserting wrapper success!");
}
#Override
public void handleFailure(Exception e) throws TestFailedException {
//TODO: add to log file, log to output and throw exception
System.out.println("Asserting wrapper failure!");
throw new TestFailedException();
}
#Override
public void handleSoftFailure(Exception e) {
//TODO: add to log file, log to output
System.out.println("Asserting wrapper soft failure!");
e.printStackTrace();
}
}
So, we can use it like that:
AssertingWrapper wrapper = new AssertingWrapper(new IDoNotOwnThisType());
AssertingType type = wrapper.doC();
AssertingType type2 = type.doF();
Output:
Asserting wrapper before operation!
doC
Asserting wrapper success!
Asserting type before operation!
doF
Asserting type success!
The full working code is here:
LIVE
The problem is, I have always to write while, try catch etc in AType and AWrapper, can I somehow reduce code duplication? In the example i provided just 3 functions per class, but in my real code I have 50+ methods. Can I somehow wrap these functions so thepart that is repeating is not duplicated?

Your problem appears to be quite complicated, and I cannot claim to have been able to successfully wrap my mind around it, but I will give it a try, because it appears to be a very interesting problem and because I happen to have some experience in dealing with situations that yours appears similar to.
Please excuse me if my answer turns out to be completely off the mark due to a misunderstanding on my part.
So, what it appears that you are looking for is a general purpose solution for injecting your own code before and after an invocation where the invocation may be to any method, accepting any number of parameters, and returning any kind of return value.
In java there exists a dynamic proxy facility, which you can find under java.lang.reflect.Proxy.
With it, you can do the following:
ClassLoader classLoader = myInterfaceClass.getClassLoader();
T temp = (T)Proxy.newProxyInstance( classLoader, new Class<?>[] { myInterfaceClass },
invocationHandler );
The invocationHandler is supplied by you, and it is of the following form:
private final InvocationHandler invocationHandler = new InvocationHandler()
{
#Override
public Object invoke( Object proxy, Method method, Object[] arguments )
throws Throwable
{
/* your pre-invocation code goes here */
/* ... */
/* invoke original object */
Object result = method.invoke( myObject, arguments );
/* your post-invocation code goes here */
/* ... */
/* return the result (will probably be null if method was void) */
return result;
}
};
So, I think you might be able to use that to solve your problem with the minimum amount of code.
Neither the creation of a dynamic proxy nor the call to method.invoke() perform terribly well, (you know, reflection is somewhat slow,) but if you are using it for testing, it should not matter.

Java - Method implementation dependent from parameter value

Consider a method
public void doSomething(String actionID){
switch (actionID){
case "dance":
System.out.print("I'm dancing");
break;
case "sleep":
System.out.print("I'm sleeping");
break;
default:
System.out.print("I've no idea what I'm doing");
}
The implementation of the method depends on the value of the parameter. Is there a more elegant way to do this, or a different design pattern to replicate the behaviour?

If the caller decides what logic is executed by passing different strings, then why not just have them call different methods:
public void doSomething(String actionID) {...}
...
doSomething("dance");
doSomething("sleep");
VS.:
public void dance() {...}
public void sleep() {...}
...
dance();
sleep();
It seems like you're unnecessarily funnelling all the calls into doSomething
But the strings might not always be literals. What if you're taking them from the console?
You could provide static mappings from the strings to the corresponding functions:
class MyClass {
private static final Map<String, Consumer<MyClass>> map = new HashMap<>();
static {
map.put("sleep", MyClass::sleep);
map.put("dance", MyClass::dance);
}
public void doSomething(String actionID) {
map.getOrDefault(actionID, MyClass::doNothing).accept(this);
}
public void dance() {
System.out.print("I'm dancing");
}
public void sleep() {
System.out.print("I'm sleeping");
}
private void doNothing() {
System.out.println("I've no idea what I'm doing");
}
}
This makes scenarios where you have a lot of switch cases a lot cleaner.

Introduce an interface, e.g.
public interface HumanState {
public void tellMeWhatYouAreDoing();
}
encapsulate the logic in different implementations
public class DancingState implements HumanState {
#Override
public void tellMeWhatYouAreDoing() {
System.out.println("I'm dancing");
}
}
public class SleepingState implements HumanState {
#Override
public void tellMeWhatYouAreDoing() {
System.out.println("I'm sleeping");
}
}
public class UnknownState implements HumanState {
#Override
public void tellMeWhatYouAreDoing() {
System.out.println("I've no idea what I'm doing");
}
}
and use a map. E.g.
public class HumanStateExample {
public static void main(String[] args) {
HumanStateExample humanStateExample = new HumanStateExample();
humanStateExample.doSomething("dance");
humanStateExample.doSomething("sleep");
humanStateExample.doSomething("unknown");
}
private final HashMap<String, HumanState> humanStateMap;
public HumanStateExample(){
humanStateMap = new HashMap<String, HumanState>();
humanStateMap.put("dance", new DancingState());
humanStateMap.put("sleep", new SleepingState());
}
public void doSomething(String action) {
HumanState humanState = humanStateMap.get(action);
if(humanState == null){
humanState = new UnknownState();
}
humanState.tellMeWhatYouAreDoing();
}
}

I'm not sure how the pattern is called, but it is very useful if you need to delegate the method call based on more than one parameter:
Create a lot of handlers where each one knows when it is responsible for handling a call. Then just loop through them and invoke the first one matching the parameter.
edit: I renamed the class from FancyParameterActionFactory to FancyParameterActionUtility: it is not a factory, the name was misleading
//Your method, but this time with a complex object, not with a simple string.
public void doSomething(FancyParameterObject fpo){
FancyParameterActionUtility.invokeOn(fpo);
}
//The utility which can handle the complex object and decides what to do.
public class FancyParameterActionUtility{
public Interface FPAHandler{
void invoke(FancyParameterObject fpo);
boolean handles(FancyParameterObject fpo);
}
//Omitted: Different implementations of FPAHandler
public static List<FPAHandler> handlers = new LinkedList<>();
static{
handlers.add(new DanceHandler());
handlers.add(new SleepHandler());
//Omitted: Different implementations of FPAHandler
}
public static void invokeOn(FancyParameterObject fpo){
for(FPAHandler handler:handlers){
if (handler.handles(fpo)){
handler.invoke(fpo);
return;
}
}
//Default-Behavior
}
}

Here is a simple implementation of the command pattern based your sample problem. I define a general AbstractCommand abstract class which contains two methods. The first method, createCommand(), instantiates a command class based on an input string name. This is how you can delegate your string input to create the right type of command. The second method is doAction(), and this is left undefined, to be implemented later on by specific concrete command classes.
public abstract class AbstractCommand {
public static AbstractCommand createCommand(String name) {
try {
String clsName = name + "Command";
Class<?> cls = Class.forName(clsName);
AbstractCommand command = (AbstractCommand) cls.newInstance();
return command;
}
catch (Exception e) {
System.out.println("Something went wrong.");
}
}
public abstract void doAction();
}
public class DanceCommand extends AbstractCommand {
public void doAction() {
System.out.println("I'm dancing");
}
}
public class TestCommandPattern {
public void doSomething(String actionID) {
AbstractCommand cmd = AbstractCommand.createCommand(actionID);
cmd.doAction();
}
public static void main(String[] args) {
TestCommandPattern test = new TestCommandPattern();
test.doSomething("Dance"); // should print "I'm dancing"
}
}
Now that this framework has been setup, you could easily add other commands for the various types of actions in your original problem. For example, you could create a SleepCommand class which would output I'm sleeping, or do whatever action you wish.

Java - Execute a class method with a specify annotation

I have a android application, but it is not relevant.
I have a class called "Front controller" which will receive some message
through it's constructor. The message, for brievity, could be an integer.
I want somewhere else to create a new controller which will execute
a method based on the integer defined above
public class OtherController {
#MessageId("100")
public void doSomething(){
//execute this code
}
#MessageId("101")
public void doSomethingElse(){
//code
}
}
The front controller could be something like this:
public class FrontController {
private int id;
public FrontController(int id){
this.id=id;
executeProperControllerMethodBasedOnId();
}
public void executeProperControllerMethodBasedOnId(){
//code here
}
public int getId(){
return id;
}
}
So, if the Front Controller will receive the integer 100, it
will execute the method annotated with #MessageId(100). The
front controller don't know exactly the class where this method
is.
The problem which I found is that I need to register somehow
each controller class. I Spring I had #Component or #Controller
for autoloading. After each controllers are register, I need to
call the properly annotated method.
How to achieve this task? In Spring MVC, I had this system
implemented, used to match the HTTP routes. How could I implement
this in a plain java project?
Any suggestions?

Thanks to Google Reflections (hope you can integrate this in your android project.)
<dependency>
<groupId>org.reflections</groupId>
<artifactId>reflections-maven</artifactId>
<version>0.9.8</version>
</dependency>
For optimisation I've added the requirement to also annotate the class with MessageType annotation and the classes should be in the same package (org.conffusion in my example):
#Retention(RetentionPolicy.RUNTIME)
#Target(ElementType.TYPE)
public #interface MessageType {
}
The OtherController looks like:
#MessageType
public class OtherController {
#MessageId(id=101)
public void method1()
{
System.out.println("executing method1");
}
#MessageId(id=102)
public void method2()
{
System.out.println("executing method2");
}
}
The implementation will look like:
public void executeProperControllerMethodBasedOnId() {
Set<Class<?>> classes = new org.reflections.Reflections("org.conffusion")
.getTypesAnnotatedWith(MessageType.class);
System.out.println("found classes " + classes.size());
for (Class<?> c : classes) {
for (Method m : c.getMethods()) {
try {
if (m.isAnnotationPresent(MessageId.class)) {
MessageId mid = m.getAnnotation(MessageId.class);
Object o = c.newInstance();
if (mid.id() == id)
m.invoke(o);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
Maybe you can optimise and build a static hashmap containing already scanned message ids.

You need to implement some of the work by yourself using reflection, I would recommend to prepare message handlers on initial phase in regards to performance. Also you possibly want to think about Singleton/Per Request controllers. Some of the ways to implement the solution:
interface MessageProcessor {
void execute() throws Exception;
}
/* Holds single instance and method to invoke */
class SingletonProcessor implements MessageProcessor {
private final Object instance;
private final Method method;
SingletonProcessor(Object instance, Method method) {
this.instance = instance;
this.method = method;
}
public void execute() throws Exception {
method.invoke(instance);
}
}
/* Create instance and invoke the method on execute */
class PerRequestProcessor implements MessageProcessor {
private final Class clazz;
private final Method method;
PerRequestProcessor(Class clazz, Method method) {
this.clazz = clazz;
this.method = method;
}
public void execute() throws Exception {
Object instance = clazz.newInstance();
method.invoke(instance);
}
}
/* Dummy controllers */
class PerRequestController {
#MessageId(1)
public void handleMessage1(){System.out.println(this + " - Message1");}
}
class SingletonController {
#MessageId(2)
public void handleMessage2(){System.out.println(this + " - Message2");}
}
class FrontController {
private static final Map<Integer, MessageProcessor> processors = new HashMap<Integer, MessageProcessor>();
static {
try {
// register your controllers
// also you can scan for annotated controllers as suggested by Conffusion
registerPerRequestController(PerRequestController.class);
registerSingletonController(SingletonController.class);
} catch (Exception e) {
throw new ExceptionInInitializerError();
}
}
private static void registerPerRequestController(Class aClass) {
for (Method m : aClass.getMethods()) {
if (m.isAnnotationPresent(MessageId.class)) {
MessageId mid = m.getAnnotation(MessageId.class);
processors.put(mid.value(), new PerRequestProcessor(aClass, m));
}
}
}
private static void registerSingletonController(Class aClass) throws Exception {
for (Method m : aClass.getMethods()) {
if (m.isAnnotationPresent(MessageId.class)) {
MessageId mid = m.getAnnotation(MessageId.class);
Object instance = aClass.newInstance();
processors.put(mid.value(), new SingletonProcessor(instance, m));
}
}
}
/* To process the message you just need to look up processor and execute */
public void processMessage(int id) throws Exception {
if (processors.containsKey(id)) {
processors.get(id).execute();
} else {
System.err.print("Processor not found for message " + id);
}
}
}

Use reflection to create classes at runtime

I have to create a list of objects, which are configured according to the name of some classes received as input.
For each object I have to call a method, which add an operation that is created dynamically.
However I don't know exactly ho to resolve the problem.
Please see an example below.
String className; // this is an input parameter
final Class<?> classType = Class.forName(className);
// here I would like to use classType instead of "?" but it gives me an error.
Task<?> task = TaskFactory.createTask((String)classType.getField("_TYPE").get(null)));
tasks.put(task, null);
task.addOperation(new Operation<classType>() { // this gives an error
#Override
public void onNewInput(classType input) { // this gives an error
System.out.println(input)
}
});

As you can see from the comments, the surrounding infrastructure and the intention are not entirely clear. However, you can achieve a certain degree of type-safety with a "helper" method that captures the type of the given Task, and allows you to work with this type internally:
public class RuntimeType
{
public static void main(String[] args) throws Exception
{
String className = "";
final Class<?> classType = Class.forName(className);
Task<?> task = TaskFactory.createTask((String)classType.getField("_TYPE").get(null));
addOperation(task);
}
private static <T> void addOperation(Task<T> task)
{
task.addOperation(new Operation<T>()
{
#Override
public void onNewInput(T input)
{
System.out.println(input);
}
});
}
}
class TaskFactory
{
public static Task<?> createTask(String string)
{
return null;
}
}
class Task<T>
{
public void addOperation(Operation<T> operation)
{
}
}
interface Operation<T>
{
void onNewInput(T input);
}