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Practical Exception Handling Example
Exceptions example from a Well House Consultants training course
More on Exceptions [link]
Source code: Bikini.java Module: J712
import java.io.*;
import java.util.*; /* Practical Exception Handling Example This is an example that opens and reads from a data file, storing information into an ArrayList and a HashMap as it stored the information it needs for a report. Exceptions used within the main code to trap program runs where no input file is specified, or the input file named doesn't exist or can't be read. And we've also used our own exception if our call to "getCountry" isn't going to be able to identify tehe origin of the request. */ public class Bikini { public static String getCountry(String Ip) { // Throws an exception if cannot resolve to a country // (IRL - use this to call www.maxmind.com's database!) // Failure - throw an exception rather than returning a value if (! Ip.startsWith("66")) { ArrayIndexOutOfBoundsException fred = new ArrayIndexOutOfBoundsException("Dunno, Mate!"); throw fred; } // Success - return a value return "Potential Googleland"; } public static void main (String [] args) { int countplace = 0, countlines = 0; int iptop; String RemoteIp; BufferedReader Suck = null; // Open the input file - deal with any issues if you can't try { Suck = new BufferedReader(new FileReader(args[0])); } catch (ArrayIndexOutOfBoundsException e) { // Failed to specify file name System.err.println ("Hey - where should I look?"); System.exit(1); } catch (Exception e) { // Name given doesn't map to a file that can be read System.err.println ("Oh Sh..dear"); System.err.println ("Contact the support team: " + e); System.exit(1); } String Stuff; // Read and store all Swindon interest by IP ArrayList<String> Iprecords = new ArrayList<String>(); // Also store a count of visits from each different IP HashMap Counters = new HashMap(); try { // In case data stream breaks while ((Stuff = Suck.readLine()) != null) { countlines ++; iptop = Stuff.indexOf(" "); RemoteIp = Stuff.substring(0,iptop); if (Stuff.indexOf("Swindon") >= 0) { // Store onto an ArrayList Iprecords.add(RemoteIp); // Also store into a HashMap // Get count so far for this IP from Hashmap Integer temp = (Integer)Counters.get(RemoteIp); // If this is an IP we have not seen before, set 0 if (temp == null) temp = new Integer(0); // Store one more than previous value into Hashmap Integer newval = new Integer(1+temp.intValue()); Counters.put(RemoteIp,newval); countplace++; } } } catch (IOException e) { System.err.println("Problem reading file"); System.exit(1); } System.out.println("Total " + countlines); System.out.println("Matched " + countplace); // And print out IP list too for (int k=0; k<Iprecords.size(); k++) { String iprecalled = Iprecords.get(k); System.out.println(iprecalled); } System.out.println("----------------"); // Print out IP list with times each occurred from the HashMap // Get the keys so that we can handle them each in turn [keyset] Set HostKeys = Counters.keySet(); // Make an iterator which can step through the keyset one by one Iterator It = HostKeys.iterator(); // "while we still have data available from the iterator ..." while (It.hasNext()) { // " ... get the next piece of data [key]" String HostNow = (String)(It.next()); int c = ((Integer)Counters.get(HostNow)).intValue(); String Country = null; try { Country = getCountry(HostNow); } catch (Exception e) { Country = "Dunno where!"; } // Print out the IP addresses and the counts alongside System.out.println((String)HostNow + " - " + c + " - " + Country); } } } /* Sample Outputs ... wizard:jn10 graham$ java Bikini Hey - where should I look? wizard:jn10 graham$ java Bikini ac_20101100 Oh Sh..dear Contact the support team: java.io.FileNotFoundException: ac_20101100 (No such file or directory) wizard:jn10 graham$ java Bikini ac_20101102 Total 170046 Matched 48 77.88.24.25 66.249.66.152 66.249.66.148 67.195.112.232 77.88.24.25 66.249.65.174 124.187.21.202 124.187.21.202 124.187.21.202 124.187.21.202 77.88.24.25 66.249.65.174 65.52.108.12 67.195.115.231 66.235.124.20 77.88.24.25 77.88.24.25 66.249.65.155 207.46.13.143 77.89.152.10 77.89.152.10 77.89.152.10 66.249.65.174 66.249.65.174 67.195.112.232 86.142.209.15 86.142.209.15 86.142.209.15 66.249.65.88 66.249.65.88 77.88.24.25 66.249.66.152 178.63.20.133 66.249.65.70 77.88.24.25 65.55.3.184 77.88.24.25 66.249.65.70 77.88.24.25 77.88.24.25 94.195.99.221 94.195.99.221 94.195.99.221 94.195.99.221 94.195.99.221 217.160.182.81 66.249.66.174 67.195.112.232 ---------------- 66.249.65.70 - 2 - Potential Googleland 124.187.21.202 - 4 - Dunno where! 77.89.152.10 - 3 - Dunno where! 66.249.66.152 - 2 - Potential Googleland 178.63.20.133 - 1 - Dunno where! 66.249.65.88 - 2 - Potential Googleland 66.249.66.148 - 1 - Potential Googleland 65.55.3.184 - 1 - Dunno where! 66.235.124.20 - 1 - Potential Googleland 217.160.182.81 - 1 - Dunno where! 66.249.65.174 - 4 - Potential Googleland 86.142.209.15 - 3 - Dunno where! 67.195.115.231 - 1 - Dunno where! 207.46.13.143 - 1 - Dunno where! 94.195.99.221 - 5 - Dunno where! 67.195.112.232 - 3 - Dunno where! 77.88.24.25 - 10 - Dunno where! 66.249.66.174 - 1 - Potential Googleland 65.52.108.12 - 1 - Dunno where! 66.249.65.155 - 1 - Potential Googleland wizard:jn10 graham$ */ Learn about this subject
This module and example are covered on the following public courses:
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