Building of Java API

Creating a Simple Hello World Backend API

In this part of the tutorial, we'll use the App Engine Maven artifact endpoints-skeleton-archetype to create a new Endpoints project. We'll then show you how to add code.

Creating and building the project

To create the Hello World backend API:

1. In a terminal window, change to the directory where you want to build the project.
   
2. Invoke the following Maven command:
   

   mvn archetype:generate -Dappengine-version=1.9.23 -Dfilter=com.google.appengine.archetypes:
   

3. Enter the number 2 to select the archetype remote -> com.google.appengine.archetypes:endpoints-skeleton-archetype from the list of App Engine archetypes.
   
4. Accept the default to use the most recent version.
   
5. When prompted to Define value for property 'groupId', enter the namespace com.example.helloworld to keep this tutorial in sync with the source files at GitHub. (The typical convention is to use a namespace starting with the reversed form of your domain name.)
   
6. When prompted to Define value for property 'artifactId', supply the project name helloworld.
   
7. When prompted to Define value for property 'version', accept the default value.
   
8. When prompted to Define value for property 'package', accept the default value.
   
9. When prompted to confirm your choices, accept the default value (Y).
   
10. Wait for the project to finish generating, then take a look at the resulting project layout:
    
    The pom.xml file contains all the configuration and dependencies needed for your backend API.
    
11. Change directories to the project's Java source directory: /src/main/java/com/example/helloworld.
    
12. Create a JavaBean class file named MyBean.java copy-paste the following code into it                               
    

    package com.example.helloworld;
    /** The object model for the data we are sending through endpoints */
    public class MyBean {
    
        private String myData;
    
        public String getData() {
            return myData;
        }
    
        public void setData(String data) {
            myData = data;
        }
    }

13. requires a browser that supports JavaScript and iframes.]</p> We'll use this JavaBean object to send data through the backend API.
    
14. Edit the file YourFirstAPI.java, replacing all of the contents with the following code:                                                                                                                     
    

    package com.example.helloworld;
    import com.google.api.server.spi.config.Api;
    import com.google.api.server.spi.config.ApiMethod;
    import com.google.api.server.spi.config.ApiNamespace;
    import javax.inject.Named;
    /** An endpoint class we are exposing */
    @Api(name = "myApi",
         version = "v1",
         namespace = @ApiNamespace(ownerDomain = "helloworld.example.com",
                                    ownerName = "helloworld.example.com",
                                    packagePath=""))
    public class YourFirstAPI {
    
        /** A simple endpoint method that takes a name and says Hi back */
        @ApiMethod(name = "sayHi")
        public MyBean sayHi(@Named("name") String name) {
            MyBean response = new MyBean();
            response.setData("Hi, " + name);
    
            return response;
        }
    }

                                                   
    
    @Api; this is where we set the configuration of the backend API.
15. Notice the @ApiMethod annotation; it allows you to configure your methods.
    Finally, notice the use of the javax.inject.Named annotation (@Named) in the sayHi method definition. You must supply this annotation for all parameters passed to server-side methods, unless the parameter is an entity type.
    
16. Build the project by invoking
    

    mvn clean install

    Wait for the project to build. When the project successfully finishes, you will see a message similar to this one:
    

    [INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------
    [INFO] Total time: 14.846s
    [INFO] Finished at: Tue Jun 03 09:43:09 PDT 2014
    [INFO] Final Memory: 24M/331M
    

Running and testing the API locally

To test the backend API locally:

1. From the main directory helloworld/, start the API in the development server as follows:
   

   mvn appengine:devserver

   Wait for the dev server to start up. When the server is ready, you will see a message similar to this one:
   

   [INFO] INFO: Module instance default is running at http://localhost:8080/
   [INFO] Jun 03, 2014 9:44:47 AM com.google.appengine.tools.development.AbstractModule startup[INFO] INFO: The admin console is running at http://localhost:8080/_ah/admin
   [INFO] Jun 03, 2014 9:44:47 AM com.google.appengine.tools.development.DevAppServerImpl doStart[INFO] INFO: Dev App Server is now running

2. Visit the APIs Explorer at this URL:
   

   http://localhost:8080/_ah/api/explorer
   

   (The Google APIs Explorer is a built-in tool that lets you send requests to a backend service without using a client app.)
   
3. Click myApi API to display the methods available from this API.
   
4. Click myApi.sayHi to display the Explorer for this method:
   
   
5. In the name field, supply your name, and click Execute and check the Response for the greeting.
   

Congratulations!

You've just built and tested your first backend API!
Next, let's build a more complete backend API wiith GET and POST methods that write to and fetch from the datastore.