Consuming RestFul services with GSON

If you want to consume the RestFul services you can check Wei Zhou’s posts in the documents section of the documentum developer network (Documentum) or check EMC RestFul Services — Clients JAVA by astone to see an example of how to consume the JSON directly from JAVA.

However, while developing the Android app I found that it was way easier to go the old Java-objects way, and you can do this by using GSON (or any other similar library).

First, you’ll need to create the POJOs/Beans for the classes; as we don’t have those (thanks EMC…) you’ll have to code them by yourself from the JSON responses (or use something like http://www.jsonschema2pojo.org/ to autogenerate them).

Once you have those (and the Gson libraries in your project) it is quite straightforward:

Reading a JSON response as an object:

DefaultHttpClient httpClient = new DefaultHttpClient();  
      
//documentum user and password  
String authorizationString = "Basic " + Base64.encodeToString((strUser + ":" + strPass).getBytes(), Base64.NO_WRAP);  
      
//request the page, here we get the main repository page  
HttpGet getRequest = new HttpGet(currentServer +"/repositories");  
//don't forget the credentials  
getRequest.setHeader("Authorization", authorizationString);  
//get the response  
HttpResponse getResponse = httpClient.execute(getRequest);  
HttpEntity getResponseEntity = getResponse.getEntity();  
Reader reader = new InputStreamReader(getResponseEntity.getContent());  
      
//use gson to get the object  
Gson gson=new Gson();  
RepositoryList repoList = (RepositoryList)gson.fromJson(reader, RepositoryList.class);  

Modify some property by sending a POST request:

DefaultHttpClient httpClient = new DefaultHttpClient();  
  
//documentum user and password  
String authorizationString = "Basic " + Base64.encodeToString((strUser + ":" + strPass).getBytes(), Base64.NO_WRAP);  
  
//setting up the POST request  
HttpPost postRequest = new HttpPost(currentServer+"/repositories/"+currentRepo+"/objects/"+strId);  
//don't forget the credentials  
postRequest.setHeader("Authorization",authorizationString);  
  
//Create the object with the property you want to modify  
RepositoryObject ro=new RepositoryObject();  
Attribute props=new Attribute();  
  
props.setSubject("new Subject");  
ro.setProperties(props);  
  
//set the header to the POST request  
postRequest.setHeader("Content-Type", "application/vnd.emc.documentum+json; charset=utf-8");  
//convert the object to json using gson  
Gson gson=new Gson();  
postRequest.setEntity(new StringEntity(gson.toJson(ro)));  
  
//do the POST  
HttpResponse postResponse = httpClient.execute(postRequest);

Note: As you can see, I’m not using service discovery although that would be the right way to do it, however, this was faster and it works as a how-to

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