I am using an open source library that is licensed under the GNU Lesser General Public License. (Hosted on sourceforge).
The library is very simple and just reads and writes to a csv file. My JSP is using it for input/output.
The download contains these files:
Am I restricted to only use the jar file or am I allowed to embed the source into my project?
Does using this library put restrictions on my project? What do I need to do to abide by the terms of the license?
Would the restrictions be different if the JSP was intended only for internal use?
Would the restrictions be different if this was a desktop application?
You are not restricted to only using the .jar, so you can put the .java files into your own project, however, any modifications you make to those .java files must be distributed in source form at the request of any user.
You must also provide the minimum requirements to allow a user to replace these files in the combined application. This means, you can distribute your code which uses the LGPL work as compiled .class files, such that the user can use your code against his own version of the LGPL work. This forbids you from "protecting" the resulting program to try and prevent such modifications.
These licensing terms only apply for applications you distribute to another person, so if you are using the app purely for internal use, you can do what you want. Any distribution requires you to abide by the conditions of the LGPL.