1. Lab 2 Primer Assignment 3 Structure File I/O More parsing and HTTP Formatting

2. Assignment Review: …so far: We explored sockets – We looked at how to connect to them, how to communicate (I/O) through them, how to parse the data through them, and briefly how data is interpreted through them We explored the idea of clients and servers – We looked at connecting to a server through telnet, making a client to connect via sockets, protocol schemes (how they understand each other), extracting information from sent messages, and multiple simultaneous user support (threads and why we need them)

3. Now: We will now extend the knowledge we’ve gained with more practice at the same principles We will add file I/O to the mix We will continue with string parsing We will add to our use of the HTTP protocol

4. Assignment 3 Structure We need to add: – File I/O to serve html files – Parsing to get key-value pairs from either the query string, body or both – Parsing to get requested resource from request – Proper HTTP responses (200 OK, 404 File Not Found, etc.) – Content-Length and Content-Type headers

5. Parsing the Query String and Requested File Use same structure as getContentLength() from Assignment 2 to find whole path/file[query] Use.indexOf(“ “, 5) to find the first space after “GET [or POST] / …” Use indexOf(“?”) to find the query string (if any) – If there is no match, indexOf() returns -1 Use.substring to get file request and query string

6. Parsing the Key-Value pairs We need to make 2 arrays: one for keys and one for values – A key-value pair should be indexed with the same value “key 1” “key 2” “key 3” “key 4” “value 1” “value 2” “value 3” “value 4” Index i=0 i=1 i=2 i=3

7. Parsing the Key-Value pairs New method:.split() – Splits a String into an array of strings based on a delimiter New class: StringTokenizer(String, delimiter) – Breaks a String into “tokens” based on delimiters – Can iterate through tokens in string

8. Parsing the Key-Value pairs String temp = "GET /index.html/?This=is&equals=string&user=foo"; String keys[]=temp.split(”&"); int length = temp2.length; String values[]= new String[length]; StringTokenizer st = new StringTokenizer(temp, “&=“); int i; for(i=0; i<length; i++){ keys[i] = st.nextToken(); values[i] = st.nextToken(); }

9. File Input/Output Java is designed for simple I/O – ALL I/O works the same; keyboard, monitor, files, sockets, etc. – All I/O can be cast to higher level objects An input/output stream can be cast to a reader/writer or a buffered I/O class – If you understand socket I/O, file I/O will be very simple There are 2 file I/O classes we will use: – File fin = new File(“/html”); – FileReader fileIn = new FileReader(“filename”);

10. File I/O: Classes File – Opens a local file – Can be used to quickly find length of a text file.length(); File fin = new File (“/path/to/file”); System.out.print(fin.length());

11. File I/O: Classes FileReader – Opens the file specified in “filename”; throws FileNotFoundException if the file cannot be opened – Use with BufferedReader BufferedReader fileIn = new BufferedReader(new FileReader(File));

12. File I/O: Basics Much like a socket, keyboard or monitor, file I/O can use the read(), readLine(), print(), println() methods to get data in and out of a file When reading from a file, the end can be determined: – When the input with readLine() is null – When the input with read() is –1 A “file pointer” keeps track of where in the file we are currently located (see example on next page) If we want to write a line where the file pointer currently is located, we will overwrite the line following the pointer. If the pointer is at the end of the file, we will write a new line

13. Final Thoughts Feel free to either refer to the sample solution, or to use it as the basis for the next assignment. That’s what it is there for. If you have questions, ask! There is nothing to gain from silence (except a worse mark)! Try this early! You have plenty of time to finish this. Do not wait until the last minute!