I am using rexster on top of Titan to visualize the graph. I could view the vertices and get the edges for each of them. But, how can i view complete graph from Titan instead of just getting details for each vertex.? I will have thousands of vertices and edges. If i have to view them for each vertex, it will be really tough. Pleas let me know, if there is a way to visualize whole graph.
Rexster's user interface isn't designed to visualize an entire graph. In fact, you will find that when graphs get sufficiently large, viewing the whole graph just isn't possible (or useful). For now though, let's set memory/usability issues aside to answer your question. You will want to use a different graph visualization tool, like Gephi or Cytoscape to visualize your graph. Both of those tools (and others you will find) can take GraphML as an input and using TinkerPop's Reader/Writer classes you can output your graph to that format.
You asked about Rexster so I assume that you were using TinkerPop 2.x and Titan versions prior to 1.0. If you were using Titan 1.0 (and thus TinkerPop 3.x), you could use the Gephi Plugin for the Gremlin Console to help make the integration more seamless.