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restRPC

<p>
	The restRPC (RPC over REST) API allows the creation of client-side remote proxy interfaces for calling methods on server-side POJOs using entirely REST.
</p>

<h5 class='topic'>Remote Interfaces</h5>
<p>
	The following example shows a remote interface:
</p>
<p class='bpcode w800'>
	<ja>@RemoteInterface</ja> <jc>// Annotation is optional</jc>
	<jk>public interface</jk> IAddressBook {

		<jk>void</jk> init() <jk>throws</jk> Exception;
	
		List&lt;Person&gt; getPeople();
	
		List&lt;Address&gt; getAddresses();
	
		<jk>int</jk> createPerson(CreatePerson cp) <jk>throws</jk> Exception;
	
		Person findPerson(<jk>int</jk> id);
	
		Address findAddress(<jk>int</jk> id);
	
		Person findPersonWithAddress(<jk>int</jk> id);
	
		Person removePerson(<jk>int</jk> id);
	}
</p>			
<p>
	The requirements for a remote interface method are:
</p>
<ul class='spaced-list'>
	<li>
		Must be public.
	<li>
		Can be called anything.
	<li>
		Can have any number of {@doc PojoCategories serializable and parsable} parameters.
	<li>
		Can return a {@doc PojoCategories serializable and parsable} value.
	<li>
		Can throw any <c>Throwables</c>.
</ul>
<p>
	Throwables with public no-arg or single-arg-string constructors are automatically recreated on the client side
	when thrown on the server side.
</p>

<h5 class='topic'>Client side</h5>
<p>
	Remote Interface proxies are instantiated on the client side using one of the following methods:
</p>
<ul class='javatree'>
	<li class='jc'>{@link oajrc.RestClient}
	<ul>
		<li class='jm'>{@link oajrc.RestClient#getRrpcInterface(Class) getRrpcInterface(Class)}
		<li class='jm'>{@link oajrc.RestClient#getRrpcInterface(Class,Object) getRrpcInterface(Class,Object)}
		<li class='jm'>{@link oajrc.RestClient#getRrpcInterface(Class,Object,Serializer,Parser) getRrpcInterface(Class,Object,Serializer,Parser)}
	</ul>
</ul>
<p>
	Since we build upon the existing <c>RestClient</c> API, we inherit all of it's features.
	For example, convenience methods for setting POJO filters and properties to customize the behavior of the 
	serializers and parsers, and the ability to provide your own customized Apache <c>HttpClient</c> for 
	handling various scenarios involving authentication and Internet proxies.
</p>
<p>
	Here's an example of the above interface being used:
</p>
<p class='bpcode w800'>
	<jc>// Create a RestClient using JSON for serialization, and point to the server-side remote interface servlet.</jc>
	RestClient client = RestClient.<jsm>create</jsm>()
		.json()
		.rootUrl(<js>"http://localhost:10000/remote"</js>)
		.build();
	
	<jc>// Create a proxy interface.</jc>
	IAddressBook ab = client.getRrpcInterface(IAddressBook.<jk>class</jk>);
	
	<jc>// Invoke a method on the server side and get the returned result.</jc>
	Person p = ab.createPerson(
		<jk>new</jk> Person(
			<js>"John Smith"</js>, 
			<js>"Aug 1, 1999"</js>,
			<jk>new</jk> Address(<js>"My street"</js>, <js>"My city"</js>, <js>"My state"</js>, 12345, <jk>true</jk>)
		)
	);
</p>
<p>
	Under the covers, this method call gets converted to a REST POST.
</p>
<p class='bpcode w800'>
	HTTP POST http://localhost:10000/remote/org.apache.juneau.examples.addressbook.IAddressBook/createPerson(org.apache.juneau.examples.addressbook.Person)
	Accept: application/json
	Content-Type: application/json
	
	[
		{
			"name":"John Smith",
			"birthDate":"Aug 1, 1999",
			"addresses":[
				{
					"street":"My street",
					"city":"My city",
					"state":"My state",
					"zip":12345,
					"isCurrent":true
				}
			]
		}
	]
</p>
<p>
	Note that the body of the request is an array.  
	This array contains the serialized arguments of the method.
	The object returned by the method is then serialized as the body of the response.
</p>

<h5 class='topic'>Server side</h5>
<p>
	There are two ways to expose remote interfaces on the server side:
</p>
<ol class='spaced-list'>
	<li>
		Extending from {@link oajr.remote.RrpcServlet}.
	<li>
		Using a <c><ja>@RestMethod</ja>(name=<jsf>RRPC</jsf>)</c> annotation on a Java method.
</ol>
<p>
	In either case, the proxy communications layer is pure REST.
	Therefore, in cases where the interface classes are not available on the client side, the same method calls can 
	be made through pure REST calls.  
	This can also aid significantly in debugging, since calls to the remote interface service can be made directly from
	a browser with no coding involved.
</p>

<h5 class='topic'>RrpcServlet</h5>
<p>
	The {@link oajr.remote.RrpcServlet} class is a simple specialized servlet with an abstract 
	<c>getServiceMap()</c> method to define the server-side POJOs:
</p>
<p class='bpcode w800'>
	<ja>@Rest</ja>(
		path=<js>"/remote"</js>
	)
	<jk>public class</jk> SampleRrpcServlet <jk>extends</jk> RrpcServlet {
	
		<jc>// Our server-side POJO.</jc>
		<jk>private</jk> AddressBook <jf>addressBook</jf> = <jk>new</jk> AddressBook();
	
		<ja>@Override</ja> <jc>/* RrpcServlet */</jc>
		<jk>protected</jk> Map&lt;Class&lt;?&gt;,Object&gt; getServiceMap() <jk>throws</jk> Exception {
			Map&lt;Class&lt;?&gt;,Object&gt; m = <jk>new</jk> LinkedHashMap&lt;Class&lt;?&gt;,Object&gt;();
	
			<jc>// In this simplified example, we expose the same POJO service under two different interfaces.
			// One is IAddressBook which only exposes methods defined on that interface, and
			// the other is AddressBook itself which exposes all methods defined on the class itself (dangerous!).</jc>
			m.put(IAddressBook.<jk>class</jk>, <jf>addressBook</jf>);
			m.put(AddressBook.<jk>class</jk>, <jf>addressBook</jf>);
			<jk>return</jk> m;
		}
	}
</p>

<h5 class='topic'>@RestMethod(name=RRPC)</h5>
<p>
	The <c><ja>@RestMethod</ja>(name=<jsf>RRPC</jsf>)</c> approach is easier if you only have a single 
	interface you want to expose.  
	You simply define a Java method whose return type is an interface, and return the implementation of that 
	interface:
</p>
<p class='bpcode w800'>
	<jc>// Our exposed interface.</jc>
	<ja>@RestMethod</ja>(name=<jsf>RRPC</jsf>, path=<js>"/addressbookproxy/*"</js>)
	<jk>public</jk> IAddressBook getProxy() {
		<jk>return</jk> addressBook;
	}
</p>

<h5 class='topic'>RrpcServlet in a browser</h5>
<p>
	If you point your browser to the servlet above, you get a list of available interfaces:
</p>
<p class='bpcode w800'>
	http://localhost:10000/remote
</p>
<img class='bordered w800' src='doc-files/juneau-rest-server.restRPC.1.png'>
<p>
	Clicking the hyperlinks on each shows you the list of methods that can be invoked on that service.
	Note that the <c>IAddressBook</c> link shows that you can only invoke methods defined on that
	interface, whereas the <c>AddressBook</c> link shows ALL public methods defined on that class.
</p>
<h5 class='figure'>IAddressBook</h5>
<p class='bpcode w800'>
	http://localhost:10000/remote/org.apache.juneau.examples.addressbook.IAddressBook
</p>
<img class='bordered w800' src='doc-files/juneau-rest-server.restRPC.2.png'>
<p>
	Since <c>AddressBook</c> extends from <c>LinkedList</c>, you may notice familiar collections
	framework methods listed.
</p>
<h5 class='figure'>AddressBook</h5>
<p class='bpcode w800'>
	http://localhost:10000/remote/org.apache.juneau.examples.addressbook.AddressBook
</p>
<img class='bordered w800' src='doc-files/juneau-rest-server.restRPC.3.png'>
<p>
	Let's see how we can interact with this interface through nothing more than REST calls to get a better idea on 
	how this works.
	We'll use the same method call as in the introduction.
	First, we need to create the serialized form of the arguments:
</p>
<p class='bpcode w800'>
	Object[] args = <jk>new</jk> Object[] {
		<jk>new</jk> CreatePerson(<js>"Test Person"</js>,
			AddressBook.<jsm>toCalendar</jsm>(<js>"Aug 1, 1999"</js>),
			<jk>new</jk> CreateAddress(<js>"Test street"</js>, <js>"Test city"</js>, <js>"Test state"</js>, 12345, <jk>true</jk>))
	};
	String asJson = SimpleJsonSerializer.<jsf>DEFAULT_READABLE</jsf>.toString(args);
	System.<jsf>err</jsf>.println(asJson);
</p>
<p>
	That produces the following JSON output:
</p>
<p class='bpcode w800'>
	[
		{
			name: <js>'Test Person'</js>, 
			birthDate: <js>'Aug 1, 1999'</js>, 
			addresses: [
				{
					street: <js>'Test street'</js>, 
					city: <js>'Test city'</js>, 
					state: <js>'Test state'</js>, 
					zip: 12345, 
					isCurrent: <jk>true</jk>
				}
			]
		}
	]	
</p>
<p>
	Note that in this example we're using JSON.  
	However, various other content types can also be used such as XML, URL-Encoding, UON, or HTML.  
	In practice however, JSON will preferred since it is often the most efficient.
</p>
<p>
	Next, we can use a tool such as Poster to make the REST call.
	Methods are invoked by POSTing the serialized object array to the URI of the interface method.
	In this case, we want to POST our JSON to the following URL:
</p>
<p class='bpcode w800'>
	http://localhost:10000/remote/org.apache.juneau.examples.addressbook.IAddressBook/createPerson(org.apache.juneau.examples.addressbook.CreatePerson)
</p>
<p>
	Make sure that we specify the <c>Content-Type</c> of the body as <c>text/json</c>.
	We also want the results to be returned as JSON, so we set the <c>Accept</c> header to 
	<c>text/json</c> as well.
</p>
<img class='bordered w400' src='doc-files/juneau-rest-server.restRPC.4.png'>
<p>
	When we execute the POST, we should see the following successful response whose body contains the returned 
	<c>Person</c> bean serialized to JSON:
</p>
<img class='bordered w400' src='doc-files/juneau-rest-server.restRPC.5.png'>
<p>
	From there, we could use the following code snippet to reconstruct the response object from JSON:
</p>
<p class='bpcode w800'>
	String response = <js>"<i>output from above</i>"</js>;
	Person p = JsonParser.<jsf>DEFAULT</jsf>.parse(response, Person.<jk>class</jk>);
</p>
<p>
	If we alter our servlet to allow overloaded GET requests, we can invoke methods using nothing more than a 
	browser...
</p>
<p class='bpcode w800'>
	<ja>@Rest</ja>(
		path=<js>"/remote"</js>,
		
		<jc>// Allow us to use method=POST from a browser.</jc>
		allowedMethodParams=<js>"*"</js>
	)
	<jk>public class</jk> SampleRrpcServlet <jk>extends</jk> RrpcServlet {
</p>
<p>
	For example, to invoke the <c>getPeople()</c> method on our bean:
</p>
<p class='bpcode w800'>
	http://localhost:10000/remote/org.apache.juneau.examples.addressbook.IAddressBook/getPeople?method=POST
</p>			
<img class='bordered w800' src='doc-files/juneau-rest-server.restRPC.6.png'>
<p>
	Here we call the <c>findPerson(<jk>int</jk>)</c> method to retrieve a person and get the 
	returned POJO (in this case as HTML since that's what's in the <c>Accept</c> header when calling from a 
	browser):
</p>
<p class='bpcode w800'>
	http://localhost:10000/remote/org.apache.juneau.examples.addressbook.IAddressBook/findPerson(int)?method=POST&amp;body=@(3)
</p>			
<img class='bordered w800' src='doc-files/juneau-rest-server.restRPC.7.png'>
<p>
	When specifying the POST body as a <c>&amp;body</c> parameter, the method arguments should be in UON 
	notation.
	See {@link oaj.uon.UonSerializer} for more information about this encoding.
	Usually you can also pass in JSON if you specify <c>&amp;Content-Type=text/json</c> in the URL parameters
	but passing in unencoded JSON in a URL may not work in all browsers.  
	Therefore, UON is preferred.
</p>
<p>
	The hyperlinks on the method names above lead you to a simple form-entry page where you can test
	passing parameters in UON notation as URL-encoded form posts.
</p>
<h5 class='figure'>Sample form entry page</h5>
<img class='bordered w800' src='doc-files/juneau-rest-server.restRPC.8.png'>
<h5 class='figure'>Sample form entry page results</h5>
<img class='bordered w800' src='doc-files/juneau-rest-server.restRPC.9.png'>