What essential classes are needed to establish a proxy server program in Java? [A proxy server acts as a mediator between the server and the client - all messages between the client and server passes through the proxy server.] Discuss how many instances of the classes are needed and for what purpose/s is/are these classes for. Note: The proxy server should only cater to one client and that the kind of stream to be established should be that of a character stream.

2. Describe (in your own words) the three models (These models are a.) User Interface Integration b.)Data Integration Model c.) Functional Integration Model) presented in integrating applications in an organization. Include in your discussion the situation(s) where the use of one model would be most appropriate over the rest.

3. What is the use of the executor's framework in Java? Where is the use of this framework more applicable, the server or the client? Explain.