In yesterday’s blog, I talked about a little known secret of vSphere MOB – the invisible embedded XML in the HTML pages. To take advantage of the secret, I created a client side REST API which was shipped in VI Java API 2.0.
Note that I call it a Client side REST, because it is different from conventional REST API whose boundary is on the wire. With the Client side REST, the boundary is on the client side over the Java API. It implies that you cannot use a Web browser to “GET” information as would you with most conventional REST API. Anyway, the difference is not big enough for you to think twice because even if you use conventional REST API, most likely you will use a wrapper layer instead of tweaking XML data directly.
The API is very powerful and easy to use, and can do almost everything the SOAP APIs can do. There are a few developers tried it and fell in love with it, but most people don’t know much about it.
When Would You Want to Use It?
As said, the Client REST API provides similar functionality as SOAP based API. The key advantages of the API are
- Super fast loading time compared with VI SDK. Already impressed by the VI Java API SOAP implementation, this API is about 20 times faster than that in loading time.
- Super simple and light-weighted. Only 4 Java classes involved and zero dependency on any third party library other than J2SE.
- XML centric so that you can easily apply XPATH, XSLT, XQuery on the data returned from the API.
- Version Neutral. It works with 2.0, 2.5, and 4.0 without any change in your code.
- Can be easily ported to other languages. I actually did a Python version and then handled it over to my colleagues. Consider the amount of code involved, it’s not a big project.
Once you are clear with these benefits, you can decide how it fits your projects. Before you make the final decision, please read on to the discussion part.
Architecture Overview
As you can see from the following figure, there are two layers: REST API layer and the managed object wrapper/cache layer. The later is built on top of the former. You can build your applications on either or both of these two layers.
The REST API layer talks to the vCenter/ESX(i) as a MOB client. It takes REST-like URL from the callers and makes HTTP calls to the server. When the responses come back, it converts them back to XML and returns to the caller.
The managed object wrapper/cache layer provides a bit higher level services, so you can speak in terms like managed object, properties, data object, etc. The caching is a little interesting here. It basically provides a caching around a wrapper. The cache holds the whole property XML so that you can retrieve multiple properties without going to the server twice.
The following diagram shows the object models. RestClient is the REST API layer. The RestManagedObject and CachedManagedObject are Managed Object wrapper/cache layer.
The ResultConverter is a helper class that you don’t even need to know, but it does the heavy lifting in the back. The challenge for the ResultConvert is that the responses of method calls do NOT have any XML embedded, therefore the code has to parse the HTML tables to XML. It can be tricky when you have tables embedded in tables for several layers.
As a long time software professional, I know how important the samples are to learn a new APIs. Let’s move onto the HelloWorld like sample.
A Sample Using Both API Layers
This is a sample included with the VI Java API that shows how you can use the API. It has two methods that demo the usage of the REST level API and managed object level API. I believe it is clear enough for me not to add any additional explanation. Click here to check out the full code from the code repository.
public class RestAppDemo
{
public static void main(String[] args) throws Exception
{
RestClient rc = new RestClient("https://8.8.8.8", "root", "pass");
runRestLevel(rc);
runMOLevel(rc);
}
public static void runMOLevel(RestClient rc) throws Exception
{
RestManagedObject si = new RestManagedObject(rc, "ServiceInstance");
System.out.println("name:" + si.getPropertyAsString("content.about.fullName"));
System.out.println(si.invoke("currentTime"));
System.out.println(si.invoke("retrieveContent"));
String allXml = si.getAllProperties();
System.out.println(allXml);
CachedManagedObject csi = new CachedManagedObject(allXml);
System.out.println("name:" + csi.getProperty("content.about.fullName"));
System.out.println("root:" + csi.getProperty("content.rootFolder"));
System.out.println("cap:" + si.getPropertyAsString("capability.multiHostSupported"));
String em_id = si.getPropertyAsString("content.eventManager");
RestManagedObject eventMgr = new RestManagedObject(rc, em_id);
System.out.println("latest evt:" + eventMgr.getPropertyAsString("latest.fullFormattedMessage"));
RestManagedObject vm = new RestManagedObject(rc, "48");
System.out.println("reload:" + vm.invoke("reload"));
CachedManagedObject cvm = new CachedManagedObject(vm.getAllProperties());
System.out.println("Roles:" + cvm.getProperty("effectiveRole"));
}
public static void runRestLevel(RestClient rc) throws Exception
{
String contentXml = rc.get("moid=ServiceInstance&doPath=content");
System.out.println(contentXml);
XPath xpath = XPathFactory.newInstance().newXPath();
String emMOR = xpath.evaluate("//eventManager/text()", new InputSource(new StringReader(contentXml)));
System.out.println("view:" + emMOR);
String lastEventXml = rc.get("moid=" + emMOR + "&doPath=latestEvent");
xpath.reset();
String eMessage = xpath.evaluate("//fullFormattedMessage/text()", new InputSource(new StringReader(lastEventXml)));
System.out.println("Latest Event: " + eMessage);
System.out.println(rc.get(null));
System.out.println(rc.get("?moid=ServiceInstance&doPath=content%2eabout"));
long start = System.currentTimeMillis();
System.out.println(rc.get("?moid=48"));
long end = System.currentTimeMillis();
System.out.println("time taken:" + (end-start));
Map para = new Hashtable();
para.put("newName", "Melody_SuSe");
System.out.println(rc.post("moid=48&method=rename", para));
Map para1 = new Hashtable();
System.out.println(rc.post("http://10.20.143.205/mob/?moid=48&method=acquireMksTicket", para1));
}
}
Discussion
Although the Client REST API works perfectly fine, it’s not supported by VMware but the open source community. The underlying MOB may change over the time. Without the secret XML, the whole stuff just doesn’t work unless much more efforts there to convert the property HTML to XML.
Having said that, it’s still a good choice for you to write small applications, especially small utilities, automation scripts, XML centric applications, etc.
Are you ready to give it a try? Visit the VI Java API project home. Everything is there.
Author: Steve Jin is the author of VMware VI and vSphere SDK (Prentice Hall), creator of VMware vSphere Java API. For future articles, please subscribe to RSS or Email, and follow on Twitter.
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