java-rest-wrapper

Java Wrapper for managing easy API logic. Basic support for Rest or parameter-based APIs.

Main features

Some main features this java wrapper have :

• Library easy to include to your project
• Configuration of the API by subclassing or by configuring web.xml
• Code of all requests are separated : one request = one file
• Supports SSO logic
• Handle XML and JSON response types. Possibility to extend with your response types.

Quick Guide

First steps

1. Include the library jar into your project library/dist/java-rest-wrapper.jar.
2. Make sure to also include all librairies inside the lib/ folder.

Way 1 : Subclassing APIHttpServlet

The APIHttpServlet is the base Servlet to use with API logic. Add a new class that extends APIHttpServlet. Put your configuration preferences inside the constructor. Here is an example :

public class SampleAPIServletWithConstructor extends APIHttpServlet {

    @Override
    public void onSetup()
    {
        // We can specify various settings for the APIHttpServlet.
        
        // Sets the parameter identifiers that will be used for specific
        // mechanics of the API.
        setParameterAlias(APIHttpServlet.PARAMETER_SSO, "ssoKey");
        
        // Sets a custom SSO class.
        setSSO(new DefaultSSO());
        
        // Sets the dispatcher.
        // The dispatcher serves as the element that will be used to
        // find which class to instantiate and use for each request type.
        Dispatcher dispatcher = new DefaultDispatcher();
        setDispatcher(dispatcher);
        
        // Sets the return schemes the system can handle.
        // By default, JSON and XML responses are managed, but
        // you may need to add some other kind of responses, like
        // default HTML or specific binary data.
        // The first element of the array is used as the default behavior.
        setReturnTypes(new DataResponse[] {
            new JSONResponse(),
            new XMLResponse()
        });
    }
    
}

You can get a fully working example on the sample project.

Way 2 : Add configuration information into web.xml

You can also use directly the DefaultAPIHttpServlet class if you specify some parameters into your web.xml file :

<servlet>
    <servlet-name>SampleAPIServletWithConfig</servlet-name>
    <servlet-class>com.doubotis.restwrapper.servlet.api.DefaultAPIHttpServlet</servlet-class>
    <init-param>
        <param-name>ssoClass</param-name>
        <param-value>com.doubotis.restwrapper.servlet.sso.SampleSSO</param-value>
    </init-param>
    <init-param>
        <param-name>dispatcherClass</param-name>
        <param-value>com.doubotis.restwrapper.sample.CasePerCaseDispatcher</param-value>
    </init-param>
    <init-param>
        <param-name>returnTypes</param-name>
        <param-value>json,xml</param-value>
    </init-param>
</servlet>

In this case, the dispatcher class and the SSO class will be instantiated from an empty constructor. You cannot set more return types when choosing the web.xml way. If you need advanced customization, it's advised to use the first way.

Setup Configuration

The base class need some information to perform API requests as you want. That means using at least a dispatcher and optionnally setup response types and SSO logic you want.

Dispatcher

A dispatcher serves as a request decision maker. Depending on request parameters found, the dispatcher will ask to the server to use different implementation files. For instance, a bootstrap Dispatcher named DefaultDispatcher serves all requests to the BaseDefaults request implementation class. This implementation class returns the current execution date of the system. You can extend Dispatcher abstract class to tell the API logic which class you want to run depending request parameters.

If you are interested by implementing a REST-based API, you can use FileResourceDispatcher that uses a file to detect what implementation class to run depending on the request path. See examples.

To set a custom dispatcher, you can :

1. Call setDispatcher(Dispatcher dispatcher) in a subclass of APIHttpServlet (override onInit() and put it inside).
2. Tell the name of the class in web.xml. In this case, the Dispatcher subclass will be instantiated with an empty constructor.

Predefined Dispatchers

The library comes with some predefined dispatchers, like DefaultDispatcher (an example of very simple dispatcher implementation), FileResourceDispatcher (a dispatcher that is based on the .txt file) and the newer : AnnotationDispatcher (works with annotations).

FileResourceDispatcher

Call the constructor and pass the .txt file that will serve as a "patron" to allow the API engine to know which class to use when a case is encountered.

FileResourceDispatcher frd = new FileResourceDispatcher("/root/paths.txt");

The txt file must be writed as this :

GET POST PUT DELETE Base /base
GET Elements /base/([^/]+)

In this example, the /base path will redirect to the Base class implementation. The implemention will works with GET, POST, PUT and DELETE HTTP methods.

AnnotationDispatcher

Just call the constructor. All the classes that extends RequestImplementation and with a REST annotation (don't forgot to set the path variable to what you want).

AnnotationDispatcher ad = new AnnotationDispatcher();

Implementation class side will work like this:

@REST(path = "/elements/([^/]+)")
public class Elements extends RequestImplementation implements IGetHandler {
    ...
}

SSO

This is optional. If you need your API be forbidden with a system of roles, you can extend the SSO abstract class to implement your own way to check. For instance, DefaultSSO returns true for every role asked, that means DefaultSSO will tell "yes" for all requests. But by overriding the hasRole(String role) method, you can modify this behavior to tell "no" when the role is not present for an API user key.

To set a custom SSO, you can :

1. Call setSSO(SSO sso) in a subclass of APIHttpServlet (override onInit() and put it inside).
2. Tell the name of the class in web.xml. In this case, the SSO subclass will be instantiated with an empty constructor.

Request Implementation Class

These are the classes referenced inside your Dispatcher subclass. They are runned depending on parameters and the decision code you write inside the Dispatcher subclass. These classes must extend RequestImplementation and potentially implements one or many of the followings :

• IGetHandler (for HTTP GET)
• IPostHandler (for HTTP POST)
• IPutHandler (for HTTP PUT)
• IDeleteHandler (for HTTP DELETE)

Override the onInit(HttpServletRequest request, HttpServletResponse resp) to include all process to open DB or files you want, and onFinish() to include all process to close DB, files or dispose things you want.

By implementing IGetHandler, your request implementation class tells that it can handle HTTP GET requests. If you doesn't implement IGetHandler and somebody try to make a HTTP GET that triggers this request implementation class, an exception will be triggered.

Throwing exceptions

Inside your request implementation classes, you can throw these exceptions if something goes wrong :

• BadRequestException : means parameters of this resource are missing or wrong.
• ForbiddenAccessException : the access to this resource is forbidden.
• InternalErrorException : the server encountered an internal error.
• NotImplementedException : the resource is not implemented yet.
• ResourceNotFoundException : the resource cannot be found. Useful when using regex for asking a specific username for instance.
• TooManyRequestsException : the resource cannot be accessed because the user have done too many requests.
• UnauthorizedAccessException : the resource is not authorized, but can be authorized by specifying some details.
• UnavailableServiceException : the resource is not available.

You can put additional message and root cause for each of these exceptions. They handle the status HTTP code and wrap the stack exception to allow external users to debug what is wrong. You can add a detailed description of the exception by using the setMessage() method.

By specifying the header X-Show-Stacktrace any user can see the entire stack exception. You can of course limit the use of this header to specific users.