代做framework、Java程序设计代写、Java代写代写、ContainerImpl代做

日期：2019-12-12 10:50

Introduction

Suppose you have a class A, which depends on class B, C, and D, and class C depends on class E and F. When

you need an instance of class A, in this case, you need to !rst create instances of class E and F, which will be

used to create an instance of class C. After that, you should create instances of class B and D. Finally, you

pass these instances to the constructor of A.

Creating instances of such classes is tedious and error-prone. The case would be much more complicated in

real world applications. It is desired that these steps can be done automatically.

Dependency injection can act as a "smart factory" to help us achieve this goal. In this assignment, you will

learn to build a tiny dependency injection framework by which you will have an impression of the internal

mechamism of dependency injection.

Requirement

To get full score in this assignment, you are required to implement an interface provided by us.

public class A {

public A(B serviceB, C serviceC, D serviceD) {

// Creating an instance of class A requires instances of class B, C, and D.

}

}

public interface Container {

<T> void register(Class<T> serviceType);

<T> void register(Class<T> serviceType, Class<? extends T> implementationType);

<T> T resolve(Class<T> serviceType);

}

Assignment of Dependency

Injection

There are three methods in this interface. The !rst two are used for registering a service type, and,

optionally, its corresponding implementation type. The last method is for getting an instance of the

speci!ed service type.

The following code snippet shows the example mentioned above, which demostrates the usage of the !rst

and the last method in the Container interface.

The second method provides the ability to associate a service type, which is usually an abstract class or an

interface, to a speci!c implementation type, which is usually a class that extends the abstract class or

implemented the interface mentioned before. Note that when multiple implementations are associate to a

service type, only the last one should take e"ect.

public class Example1 {

public static void main(String[] args) {

// Create an instance of container

Container container = new ContainerImpl();

// Register classes to the container

container.register(A.class);

container.register(B.class);

container.register(C.class);

container.register(D.class);

container.register(E.class);

container.register(F.class);

// Get an object from container

A aObject = container.resolve(A.class);

}

}

public class Example2 {

public static void main(String[] args) {

// Create an instance of container

Container container = new ContainerImpl();

// Associate A with AImpl1

container.register(A.class, AImpl1.class);

// Get an object from container

// Here aObject shoule be an instance of AImpl1

A aObject = container.resolve(A.class);

// Associate A with AImpl2

container.register(A.class, AImpl2.class);

// Get an object from container

// Here aObject shoule be an instance of AImpl2

A aObject = container.resolve(A.class);

}

}

Dependencies can be speci!ed by parameters in the constructor, or !elds with @Inject annotation. Here is

an example.

When dependencies can not be found, an ServiceNotFoundException should be thrown.

For simplicity, we guarantee that, in our test cases for grading:

No cyclic dependency would occur

To be rigorius, you are required to carefully check the arguments before further processing. An

IllegalArgumentException should be thrown if one of the following cases happen:

Null argumnet value(s) for each method

Register an interface or an abstract class for serviceType in the register method with one

parameter, or for implementationType in the register method with two parameters.

Materials Provided

Container.java: The interface to implement

ServiceNotFoundException.java: The exception to be thrown when a service can not be found

Inject.java: The annotation used to specify dependency

Submission

You should create a public class named ContainerImpl which implements the interface Container, and

upload the !le ContainerImpl.java to Sakai

You will GET A ZERO if one of the following happens:

File name is not identical to the requirement (e.g., containerImpl.java, ContainerImpl.Java)

Compilation fail

Plagiarism

public class A {

private B bDep;

@Inject

private C cDep;

public A(B bDep) {

this.bDep = bDep;

}

}