THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
<binding.rest> IntroductionThe Tuscany Java SCA runtime supports Representational State Transfer (REST) services invocations via the <binding.rest> extension. Tuscany REST binding leverage JAX-RS Standards based annotations to map business operations to HTTP operations such as POST, GET, PUT and DELETE and utilizes Tuscany Databindings to provide support for different wire formats such as JSON, XML, Binary, etc shielding the application developer from contaminating his business logic with code to handle payload production/transformation details. Using the Tuscany REST bindingThe primary use of the REST binding is to provide services over HTTP in a distributed fashion. Services are items that have data types and a defined business interfaces such as shared collections. Examples of shared collections includes shopping carts, telephone directories, insurance forms, and blog sites. These collections of items can be added, retrieved, updated, and deleted using the 4 basic actions of the HTTP protocol:
The simplest way to use the HTTP binding is to declare a resource that can be shared over the web via HTTP and provide an HTTP address where one can access the resource. This resource is declared in an SCA composite file which describes the SCA domain.
<component name="CatalogServiceComponent">
<implementation.java location="content"/>
<service name="Resource">
<tuscany:binding.http uri="http://localhost:8085/webcontent"/>
</service>
</component>
No further implementation is needed with a resource. It is served on the web like any other static web content. The HTTP binding can also declare a business service that can be shared over the web and provide an HTTP address where one can access the service. This resource is declared in an SCA composite file which describes the SCA domain.
<component name="HTTPBindingComponent">
<implementation.java class="org.apache.tuscany.sca.binding.http.TestBindingImpl"/>
<service name="TestBindingImpl">
<tuscany:binding.http uri="http://localhost:8085/httpbinding"/>
</service>
</component>
Another way of implementing an HTTP service is to use a collection interface that matches the actions of the HTTP protocol. In this case, the methods must be named post, get, put, and delete. Tuscany ensures that the proper method is invoked via the request and response protocol of HTTP:
public class TestGetImpl {
public InputStream get(String id) {
return new ByteArrayInputStream(("<html><body><p>This is the service GET method, item=" + id + "</body></html>").getBytes());
}
}
So using the common verbs of HTTP and Java object serialization, one can implement services and run them anywhere the HTTP protocol is implemented. The service developer or implementer simply creates methods for post, get, put, and delete, and a business collection such as a shopping cart, telephone directory, insurance form, or blog sites can be created. See the Tuscany module binding-http-runtime for complete examples. Advanced Features of the Tuscany HTTP BindingHTTP Conditional Actions and Caching using ETags and Last-ModifiedThe HTTP specification provides a set of methods for HTTP clients and servers to interact. These methods form the foundation of the World Wide Web. Tuscany implements many of these methods a binding interface to a collection. The main methods are:
The HTTP specification (HTTP 1.1 Chapter 13 - Caching) also provides a mechanism by which these methods may be executed conditionally. To perform conditional methods, an HTTP client puts 3 items in the HTTP request header:
The complete list of predicates is given in the HTTP specification. The most common use of conditional methods is to prevent two requests to the server instead of one conditional request. For example, a common scenario is to check if an item has been modified, if not changed update it with a new version, if changed do not update it. With a conditional PUT method (using the IfUnmodifed predicate and a LastModified date), this can be done in one action. Another common use is to prevent multiple GETs of an item to ensure we have a valid copy. Rather than doing a second request of a large item, one can do a conditional GET request (using an IfModified predicate and a LastModified date), and avoid the second request if our object is still valid. The server responds with either a normal response body, or status code 304 (Not Modified), or status code 412 (precondition failed). Tuscany implements the logic to move these caching items to and from the HTTP request and response headers, and deliver them to the collection implementation. The items are delivered to a user implementation via a serializable object called CacheContext. This object contains the value of the ETag, the LastModified value, and any predicates. It is up to the implementer of a collection to provide the correct server logic to act on these predicates. The CacheContext class is found in found in the Tuscany module package org.apache.tuscany.sca.binding.http. To implement conditional actions on your service, the developer or implementer implements any of the condional HTTP actions: conditionalPost, conditionalGet, conditionalPut, or conditionalDelete. Tuscany automatically routes a request with proper request header fields (ETag, LastModified, and predicates) to the proper collection method. For example, the TestBindingCacheImpl class in package org.apache.tuscany.sca.binding.http implements a server collection which pays attention to conditional methods. Notice that this collection implements conditionalGet, conditionalPut, conditionalPost, and conditionalDelete methods as well as get, put, post, delete. The server collection can look at the CacheContext obect to determine whether an item or a status code should be returned. In this example code, the conditionalGet checked the If-Modified predicate and determines whether the item is not modified and if so, throws a NotModifiedException.
public InputStream conditionalGet(String id, HTTPCacheContext cacheContext)
throws NotModifiedException, PreconditionFailedException {
if (cacheContext != null) {
if (cacheContext.ifModifiedSince) {
if ((id.equals("1"))
&& (0 > cacheContext.lastModifiedDate
.compareTo(new Date())))
throw new NotModifiedException("item 1 was modified on "
+ new Date());
}
...
...
For a full example of all conditional methods and many combinations of predicates, one can look to the module http-binding unit tests to understand how these conditional request work. The HTTPBindingCacheTestCase contains 36 tests of all 4 HTTP conditonal methods. Various predicates are tested with various ETags and LastModified fields. The fields are tested in both the positive and negative cases. Here is a complete list of the tests:
Similarly, there are 9 tests each for DELETE, POST, and PUT, making a total of 36 test cases. |