Red Hat
Jan 11, 2017
by Christina Lin
API plays a huge part in modern integration architecture design, a good design will allow your application to thrive, a bad design will end up on the cold stone bench and eventually vanishes :(....
Well, to avoid this tragic happens to our APIs, there are certain guidelines that we might want to consider to follow, I know there are lots of debates out there on the best practice of API design, and I don't think it will ever end. It is really depending on many different factors, mostly dominate by the size and complexity of the integration solution, and the company culture. And many of them are related to how to manage it instead of designing. (Of course there are many others like API security, how to do versioning and all these sorts of things. These are more closely related to API management, that I will not cover in this post. )

This is what I think is a good API,

1. Intuitive-  It must be easy to understand and use without documentations.
2. Stable-  Not only it should be running but with good performance too.
3. Demands -  Creating useful functionally, no matter how nicely your API is documented, how easy it is to use, it people don't need it, they won't call it.

The second one, is mostly depend on how robust your code is, the DEVOPS process, how the IT infrastructure is built and so on. And third one is a much harder question to answer, so I am going to skip these two first and focus on ONE, Intuitive. Here are just couple of best practices of that I think that can make APIs more intuitive , and how it's done in Camel. (RESTFul API for strictly speaking, the technology the most people use is the standard.)
  • Simply but concrete naming for the URI.
    • Common rules, use nouns instead of verbs, that describe the content the API is providing, such as customer, account and product etc.  In Camel the place to define it is in the REST DSL, it allows developer to define REST services in it's application. Define the name of the API in the URI and have several layers of API description.
                <get uri="customer/{customerid}">
             <to uri="direct:getCustomerinfo"/>
           </get>
           <get uri="product/{id}">
             <to uri="direct:productInventory"/>
           </get>
           <get uri="account/profile/{acctid}">
             <to uri="direct:getprofile"/>
           </get>
    • From the architectural stand point, one of the good thing about Camel and Fuse/Fuse Integration Service. You naturally create these independent chunks of service, that either connects to a datasource (or multiple if you want, but that does not quite fit in the sprits of doing microservices.) and then becomes a microservice. Or you can use it to create a service that compose/orchestrate APIs for the consumer.                     
  • Use HTTP Method for CRUD if possible 
    • Instead of creating four different names with the verbs that we normally do in webservice back in the days, take advantages of the HTTP method, that is ready there and the HTTP header actually maps to different operations that you need to do, In Camel DSL, it is very simple to define it, 
      • READ -> GET
      • CREATE -> PUT
      • UPDATE -> POST
      • DELETE -> DELETE
                 <rest path="/account">
            <get uri="profile/{acctid}">
                <to uri="direct:getprofile"/>
            </get>
            <put uri="profile/{acctid}">
                <to uri="direct:createprofile"/>
            </put>
            <post uri="transfer/{acctid}/">
                <to uri="direct:dotransfer"/>
            </post>
            <delete uri="profile/{acctid}">
                <to uri="direct:deleteprofile"/>
            </delete>
           </rest>
    • Not only it eliminates the whole team to agree upon naming of the actions, and since it's globally recognized standard, consumers will find it easier to understand.  
    • Make the most out of HTTP Errors, 
      • Wrapping your own error is good, but think about this, when a consumer gets response from the API, what is the first content it get? The HTTP response header, instead of processing the entire payload (not restricting to error, there are several successful status code too).  
      • Here are the list of http status codes, there are a couple of then that are commonly used in RESTApi, For instance, here are some of the common one used in RESTFul API

    HTTP Code
    HTTP Methods
    Description (From Wiki page)
    200
    GET, DELETE
    Standard response for successful HTTP requests. The actual response will depend on the request method used.
    201 Created
    PUT, POST 
    The request has been fulfilled, resulting in the creation of a new resource.
    202 Accepted
    POST, PUT, DELETE
    The request has been accepted for processing, but the processing has not been completed.
    400 Bad Request
    GET, POST, PUT, DELETE
    The server cannot or will not process the request due to an apparent client error
    401 Unauthorized
    GET, POST, PUT, DELETE
    Similar to 403 Forbidden, but specifically for use when authentication is required and has failed or has not yet been provided.
    403 Forbidden
    GET, POST, PUT, DELETE
    The request was a valid request, but the server is refusing to respond to it.
    404 Not Found
    GET, POST, PUT, DELETE
    The requested resource could not be found.
    408 Request Timeout
    GET, POST, PUT, DELETE
    The server timed out waiting for the request.
    409 Conflict
    PUTPUTDELETE
    Indicates that the request could not be processed because of conflict in the request.
    500 Server Error
    GET, POST, PUT, DELETE
    A generic error message, given when an unexpected condition was encountered and no more specific message is suitable.
    503 Service Unavailable
    GET, POST, PUT, DELETE
    The server is currently unavailable (because it is overloaded or down for maintenance). Generally, this is a temporary state.
      • In Camel, you can set the value in header to return the HTTP status code
    <setHeader headerName="camelhttpresponsecode">
                  <constant>400</constant >
               </setHeader>

    • Setting the right granularity of data and use common data format,
      • I don't believe in ONE SIZE FITS ALL data model when it comes to providing information to various consumer, the amount of information can be shown in a mobile device screen, an smart watch or a desktop computer is definitely different. 
      • Camel has capability for you to automatically transform the data from POJO into the format that you wanted by specifying the output, or you can simple so marshaling with various data format Camel supported or do a little extra processing with the Data Mapper transform component. 
                   The binding mode: 
                   <restConfiguration  bindingMode="json" />
    Binding ModeDescription
    off
    Binding is turned off. This is the default option.
    auto
    Binding is enabled and Camel is relaxed and support json, xml or both if the needed data formats are included in the classpath. Notice that if for example camel-jaxb is not on the classpath, then XML binding is not enabled.
    json
    Binding to/from json is enabled, and requires a json capabile data format on the classpath. By default Camel will use json-jackson as the data format. See the INFO box below for more details.
    xml
    Binding to/from xml is enabled, and requires camel-jaxb on the classpath. See the INFO box below for more details.
    json_xml
    Biding to/from json and xml is enabled and requires both data formats to be on the classpath. See the INFO box below for more details.
                      
                  Or DataFormat Marshaling (Don't forget to add the dependency of the converting libraries)
                   <marshal ref="transform-json">

                <json library="Jackson"/>
             </marshal>

                      Or Data Mapper transform (Dozer)
                   See my previous posts
                   
    • Automatic generated documentation.
      • One of the nice handy little tricks when doing API in Camel with REST DSL, you can simply integrate it with Camel swagger java components. It will expose the API in swagger format. 
      • In Camel, don't forget to first to add the dependency in your maven pom,  
    <dependency>
         <groupId>org.apache.camel</groupId>
         <artifactId>camel-swagger-java</artifactId>
         <version>x.x.x</version>
         <!-- use the same version as your Camel core version -->
    </dependency>

    And inside the Camel context, when setting up the rest configuration, simply add the API related configuration into it.
                
                <restConfiguration apiContextPath="api-docs" bindingMode="json"
                     component="servlet" contextPath="/demos">
                      <apiProperty key="cors" value="true"/>
                      <apiProperty key="api.title" value="Healthcare demo clinical API"/>
                      <apiProperty key="api.version" value="1.0.0"/>
                </restConfiguration>

    In summary this is the diagram that maps to Camel and best practices,


    Thanks!
    Original Post