There isn't a single class that will do this for you. Your basic algorithm will involve reading the file contents and then searching the data for the target text.
There are several ways you could read the file but I would suggest using a BufferedReader (which requires creating another Reader object, maybe FileReader since you can just give that the file name). BufferedReader provides a readLine() method which gives you a String to work with.
Once you have the string you can use the indexOf() method from the String class to find your target text.
Of course you'll need a loop for reading a line at a time from the file.
Note that if you are using the default character encoding. If you aren't then you'll need to create your own InputStreamReader and specify the character encoding.