I have 3 simple classes:
public abstract class Container implements WritableComparable<Container> {} //empty
public class WeightedEdge extends Container { ... }
public class NodeWeightContainer extends Container { ... }
The Map phase was configured as such
JobConf createGraphPConf = new JobConf(new Configuration());
Job job = new Job(createGraphPConf);
...
createGraphPConf.setMapOutputValueClass(Container.class);
However I am receiving this error:
java.io.IOException: Type mismatch in value from map: expected org.hadoop.test.data.util.Container, recieved org.hadoop.test.data.WeightedEdge
at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:1018)
at org.apache.hadoop.mapred.MapTask$OldOutputCollector.collect(MapTask.java:591)
at org.hadoop.test.map.CreateGPMap.map(CreateGPMap.java:33)
at org.hadoop.test.map.CreateGPMap.map(CreateGPMap.java:19)
at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:50)
at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:435)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:371)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:210)
Why I can't return a subclass of a class that was defined in the configuration? Is there a way around it? The problem is that my Map phase has to emit two distinct object types.
You can not return a subclass of a class that was defined in the configuration because Hadoop explicitly checks class type specified in setMapOutputValueClass and the type it receives from Mappers.
It does so because it needs to serialize/deserialize objects you emit from mappers. When it performs deserialization it creates new object of type that is specified in setMapOutputValueClass call and then uses methods of WriteableComparable interface to fill newly created object with data.
To be able to emit different object types you may define container non-abstract class and place actual object and its type identifier inside
public enum ELEM_TYPE { WE, WECONTAINER }
public class Container implements WritableComparable<Container>
{
ELEM_TYPE type; //actual element type -
// WeightedEdge or NodeWeightContainer
object value;
//WritableComparable implementation
// that casts value to the appropriate type
}
public class WeightedEdge { ... }
public class NodeWeightContainer { ... }
I faced the same problem today. There is a Writable class org.apache.hadoop.io.GenericWritable which can be used to address this problem. You need to extend the class and implement an abstract method:
public class Container extends GenericWritable {
private static Class[] CLASSES = {
WeightedEdge.class,
NodeWeightContainer.class,
};
protected Class[] getTypes() {
return CLASSES;
}
}
public class WeightedEdge implemets Writable {...}
public class NodeWeightContainer implements Writable {...}
Now you can use the class Container as the output value type of your mapper.
Important: Your actual map output classes (WeightedEdge and NodeWeightContainer) must implement the Writable interface.
Related
In my application i configured structuremap like
public class DefaultRegistry : Registry {
#region Constructors and Destructors
public DefaultRegistry() {
Scan(
scan => {
scan.Assembly("Eterp.Data.ErpCore");
scan.Assembly("Eterp.Data.Seed");
scan.Assembly("Eterp.Application.ErpCore");
scan.TheCallingAssembly();
scan.WithDefaultConventions();
});
ForConcreteType<AclAuthorizationManager>().Configure.Ctor<IResourceOperationAppService>()
}
#endregion
}
And i have class
public class AclAuthorizationManager : ClaimsAuthorizationManager
{
private readonly IResourceOperationAppService _resourceOperationAppService;
public AclAuthorizationManager(IResourceOperationAppService resourceOperationAppService)
{
_resourceOperationAppService = resourceOperationAppService;
}
public override bool CheckAccess(AuthorizationContext context)
{
var isCurrentUserAuthorized = context.Principal.Identity.IsAuthenticated;
return isCurrentUserAuthorized && _resourceOperationAppService.CanAccessResource(context.Action.FirstOrDefault().Value, context.Principal.Claims);
}
}
This class is custom claim authorization class using in my application, but when i exceuting the application,i am getting an error which related to lack of parameter required by the constructor, ( This class has constructor with parameter type IResourceOperation). but i already configured all the details in structureMap . i am sure that my structuremap configuration is working 100% well expect the creation of this AclAuthorizationManager class.because i am able to to apply DI in other classes.
What is wrong part in my code?
in my experience when you specify the type constructor must say that inherits from the interface.
Therefore, you should replace this line:
ForConcreteType<AclAuthorizationManager>().Configure.Ctor<IResourceOperationAppService>()
By:
ForConcreteType<AclAuthorizationManager>().Configure.Ctor<IResourceOperationAppService>().Is<ResourceOperationAppService>()
Where is the implementation ResourceOperationAppService IResourceOperationAppService.
I have an Interface defined as:
public interface DocExporter{
public void exportDoc();
}
with two implementing classes defined as:
#Service(value="docExporter")
#Scope(value="BeanDefinition.SCOPE_PROTOTYPE)
public class PdfDocExporter implements DocExporter{
public void exportDoc(){
// do Pdf Export stuff
}
}
AND
#Service(value="docExporter")
#Scope(value="BeanDefinition.SCOPE_PROTOTYPE)
public class ExcelDocExporter implements DocExporter{
public void exportDoc(){
// do Excel Export stuff
}
}
So can I say like :
#Name("docExportReporter")
#Scope(ScopeType.EVENT)
public class DocExportReporter {
#In("#{docExporter}")
private DocExporter pdfDocExporter;
#In("#{docExporter}")
private DocExporter excelDocExporter;
#Asynchronous
public void reportGen(){
**excelDocExporter.exportDoc()** // THIS THROWS Seam Exception #In attribute requires a not null value
}
}
I am new to Seam with Spring and would like to know if in both impl classes #Service would have values as "docExporter" (name of interface) or would it be like "pdfDocExporter" "excelDocExporter" ?
And with the above, I get #In attribute requires a non null value exception when using pdfDocExporter or excelDocExporter objects within the reportGen async method. Can two implementations of an interface be declared in a third class and work fine
with Seam #Asynchronous annotation ?
You cannot have two components with the same name, otherwise Seam would not know which one to inject. Use two different names.
All tutorials I've read till now about Singleton pattern were as below :
public sealed class Singleton
{
private static readonly Singleton instance = new Singleton();
private Singleton(){}
public static Singleton Instance
{
get
{
return instance;
}
}
}
but I already have a class in a assembly that I need to just have one instance of it during application lifetime . I don't know how to use pattern mentioned above .
for example suppose there is a class X in dll named Y . is the code below correct :
public sealed class Singleton
{
private static readonly Y.X instance = new Y.X();
private Singleton(){}
public static Y.X Instance
{
get
{
return instance;
}
}
}
is this a true singleton ? if not , what is a correct way to handle this situation ?
No its not the singleton pattern. The fact that you are calling new Y.X() means anyone can call it. This does not specifically disallow new instances of Y.X()
However the code is okay if you need to make sure that you refer to only one instance of Y.X in your application. Then you can get it by calling Singleton.Instance.
This is in fact the Factory pattern (A class dedicated to creating objects), and I would suggest you call the class XFactory or something similar, instead of singleton.
I would use something like :
public static class Singleton<T>
where T : new()
{
private static readonly Lazy<T> instance = new Lazy<T>();
public static T Instance
{
get
{
return instance.Value;
}
}
}
The idea is to use Generics in order to allow specify any type as type parameter.
The lazy is just an improvement to instantiate the actual instance of the object.
Please note that this won't disallow creating instances of T directly...
Is there a way to override an abstract class's method signature which uses <T> with a ClassName so I can pass an object by reference without recasting it?
For example, I have a bunch of Object Managers. I want them all to contain a .Save(Object) method which will perform the appropriate save action based on the object state (Insert, Update, Delete, etc).
I was trying to create a base class which contains these methods:
protected virtual bool Update<T>(ref T _object) where T : ObjectBase
{
throw new NotImplementedException();
}
public virtual bool Save<T>(ref T _object) where T : ObjectBase
{
// Figure out which action to take based on _object's state and execute it
}
And I wanted my inherited classes to define the methods using something like this:
public override bool Update<Consumer>(ref Consumer _object)
{
return _service.UpdateConsumer(ref _object);
}
My problem is that I can't specify that <T> will now be <Consumer>, and by keeping it at <T> I can't pass it by ref
Instead of making the methods themselves generic, you should make the entire base class generic.
For example:
public abstract class ObjectManager<T> where T : ObjectBase {
protected abstract bool Update(T obj);
}
Each concrete ObjectManager should inherit ObjectManager of the type that it manages, like this:
public class ConsumerManager : ObjectManager<Consumer> {
protected override bool Update(Consumer obj) {
...
}
}
Note, by the way, that your parameters should almost definitely not be passed ref.
You only need to ref keyword if you want to change the caller's variable to refer to a different instance.
For more information, see here.
I know singleton class is not supporting in Flex.Because it does not access private constructor.
But i want to make a class is singleton class. Please anyone can explain with example.
Thanks,
Ravi
A singleton is a class of which only one instance will be created. This instance will be shared by all other code in the program.
A singleton in the strictest sense is not supported in ActionScript because a constructor cannot be marked private. Consequently, additional instances of the class could be created elsewhere in the program. With the following trick, you can ensure that the constructor is only called by the singleton class itself:
package {
public final class Singleton {
private static var instance:Singleton = new Singleton();
public function Singleton() {
if( Singleton.instance ) {
throw new Error(
"Singleton and can only be accessed through Singleton.getInstance()" );
}
}
public static function getInstance():Singleton {
return Singleton.instance;
}
}
}