What is the difference between a Seam and a Mock?

Its being a few months since I am working with java legacy code, this are some of the things I am dealing with:

• 0% test coverage.
• Huge functions in occasions I even saw some with more than 300 lines of code.
• Lots of private methods and in occasions static methods.
• Highly tight coupled code.

At the beginning I was very confused, I found difficult to use TDD in the legacy. After doing katas for weeks and practicing my unit testing and mocking skills, my fear has decreased and I feel a bit more confident. Recently I discovered a book called: working effectivelly with legacy, I didn't read it, I just had a look at the table of contents and I discovered something that is new for me, The Seams. Apparently this is very important when working in the legacy.

I think that this Seams could help me alot in breaking dependencies and make my code testeable so I can increase the code coverage and make my unit testing more precise.

But I have a lot of doubts:

• Can somebody explain me the difference between a seam and a mock?
• Do Seams, break TDD rules in what regards not touching production code, before is tested?
• Could you show me some simple example that compares a Seam and a Mock?

Below I would like to paste an example I did today where I tried to break a dependency with the goal of making the code testeable and finally increasing test coverage. I would appreciate if you could comment a bit if you see some mistakes?

This is how the legacy code looked like at the beginning:

public class ABitOfLegacy
{
    private String sampleTitle;
    String output; 

    public void doSomeProcessing(HttpServletRequest request) {
    String [] values = request.getParameterValues(samp