Java XML解析问题

Question

I am trying to parse this java XML http://www.bnr.ro/nbrfxrates.xml and i want to extract the rate of the chosen curency, this is what I have done so far and it is not working... Can you tell me what the the right way to get to the currency rate and print it out inside the switch? ps: the xml is loaded using:

public static void main(String[] args) throws SAXException, IOException  {
    URL oracle = new URL("http://www.bnr.ro/nbrfxrates.xml");
    URLConnection yc = oracle.openConnection();
    BufferedReader in = new BufferedReader(new InputStreamReader(
                            yc.getInputStream()));
    String inputLine;
    while ((inputLine = in.readLine()) != null) 
        System.out.println(inputLine);
    in.close();





Scanner keyboard = new Scanner(System.in);
    System.out.println("What currency rate do you need?");
    String myString;
    myString = keyboard.nextLine();
    System.out.println("myint: " + myString);

    String ales = myString;

    switch(ales ){
        case "USD":
           final Pattern pattern = Pattern.compile("<Rate>(.+?)</Rate>");
           final Matcher matcher = pattern.matcher("<Rate></Rate>");
            matcher.find();
            System.out.println(matcher.group(1));

            break;


        default:
            System.out.println("We don't know");

Answer 1

without XML parsing you could change your code to something like this - this will extract the correct currency based on regex alone:

import java.net.*;
import java.io.*;
import java.util.*;
import java.util.regex.*;

public class currency {
public static void main(String[] args) throws Exception  {
    URL oracle = new URL("http://www.bnr.ro/nbrfxrates.xml");
    URLConnection yc = oracle.openConnection();
    StringWriter sw = new StringWriter();
    PrintWriter pw = new PrintWriter(sw);
    BufferedReader in = new BufferedReader(new InputStreamReader(
                            yc.getInputStream()));
    String inputLine;
    while ((inputLine = in.readLine()) != null) { 
        System.out.println(inputLine);
        pw.println(inputLine);
    }
    in.close();
    pw.close();
    sw.close();

    String data = sw.toString();

    Scanner keyboard = new Scanner(System.in);
    System.out.println("What currency rate do you need?");
    String myString;
    myString = keyboard.nextLine();
    keyboard.close();
    System.out.println("myint: " + myString);

    String ales = myString;

    Pattern pattern = Pattern.compile("<Rate currency=\""+ales+"\">(.+?)</Rate>");
    Matcher matcher = pattern.matcher(data);
    matcher.find();
    System.out.println(matcher.group(1));
    System.out.println(Double.valueOf(matcher.group(1)));
  }
}

Of cause keeping XML as string is not the best of ways to do this - as is parsing by regex.

But you could give it a try and optimize from there. Like: Putting the currencies into a map and then using this for further procesing:

Map<String,Double> currencies = new HashMap<String,Double>();
    Pattern pattern = Pattern.compile("<Rate currency=\"([^\"]{3})\">(.+?)</Rate>");
    Matcher matcher = pattern.matcher(data);
    int pos = 0;
    while(matcher.find(pos)) {
      System.out.println("Found: " + matcher.group(1) + ": " + Double.valueOf(matcher.group(2)));
      currencies.put(matcher.group(1), Double.valueOf(matcher.group(2)));
      pos = matcher.end();
    }

    Scanner keyboard = new Scanner(System.in);

    boolean ok = true;
    while(ok) {
      System.out.println("What currency rate do you need? (QUIT to quit)");
      String cur = keyboard.nextLine();
      System.out.println("Rate for " + cur + " is " + currencies.get(cur));
      if("QUIT".equalsIgnoreCase(cur)) {
        ok = false;
      }
    }    
    keyboard.close();