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The BrowserDatabase Class

So far we can represent a section of the browscap.ini file. Our next need is to read and parse the file itself, construct a number of BrowserPattern objects as necessary, and search and weigh them to match a particular browser's USER-AGENT string. This is the task of our BrowserDatabase class, which represents the database of web clients loaded from the file:

	
package com.wrox.browser;

import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.ArrayList;
import java.util.Iterator;

class BrowserDatabase {

We naturally need to store our BrowserPatterns. Often we just need to be able to iterate through them, but when we have a pattern with a parent property we will need to be able to look up a BrowserPattern by name. In this case we will store them in a HashMap, with the USER-AGENT pattern as the key. We can easily obtain a Collection containing just the BrowserPatterns by calling HashMap's values() method. We also keep a reference to the default browser, since we will often require access to it:

private HashMap browserMap = new HashMap();
private BrowserPattern defaultBrowserPattern;

protected BrowserDatabase(InputStream is) throws BrowserException {

We read the data one line at a time, constructing BrowserPattern instances as required. When we read a line there are three possibilities:

• It is a comment or blank line
• It starts a new section, being enclosed within [ and ] characters
• It specifies a property name-value pair for the current browser

To keep track of this, we keep a reference to the current BrowserPattern as we go through the file:

BrowserPattern currentBrowser = null;

We start by opening the browscap.ini file for reading:

BufferedReader reader =
	new BufferedReader(new InputStreamReader(is));

try {
	String line, trimLine;
	while ((line = reader.readLine()) != null) {
		trimLine = line.trim();
		if ((trimLine.equals("")) || (trimLine.startsWith(";"))) {
			continue;
		}

If we are starting a new section, we create a new BrowserPattern and keep it as the current pattern:

if ((trimLine.startsWith("[")) && (trimLine.endsWith("]"))) {
	String browserLine =
		trimLine.substring(1, trimLine.length()-1);
	currentBrowser = new BrowserPattern(browserLine);

The new BrowserPattern can then be stashed away in our HashMap. We use the USER-AGENT string (browserLine) as the key since that is the term we want to be able to use to look BrowserPatterns up:

  browserMap.put(browserLine, currentBrowser);
  continue;
}

A browser property line is treated by separating it into the name and value parts, and storing that in the current BrowserPattern. We take care to convert all property names to lower case, and to check for property values starting with a # character (denoting an integer value):

	if (currentBrowser != null) {
		int equalsSign = trimLine.indexOf('=');
		if (equalsSign != -1) {
	
			String name = trimLine.substring(0,equalsSign)
				.toLowerCase();
			String value = trimLine.substring(equalsSign+1,
				trimLine.length());
	
			if (value.charAt(0) == '#') {
				value = value.substring(1);
			}
			currentBrowser.addProperty(name, value);
		}
	}
}

Finally, we must remember to close the input data:

	reader.close();
	is.close();
} catch (IOException e) {
		throw new BrowserException
			("Problem reading browser capabilities file");
}

and retrieve our reference to the default browser settings:

	defaultBrowserPattern = (BrowserPattern)
	  browserMap.get("Default Browser Capability Settings");
	if (defaultBrowserPattern == null) {
	  throw new BrowserException("No default browser settings found");
	}
}

With our database constructed, we can search it. This functionality is split into two methods:

• performSearch()
  Takes a USER-AGENT string and performs the actual search through the database, returning the BrowserPattern that best matches it.
• lookup()
  Returns a BrowserInfo object representing that browser, suitable for being made available to the rest of a web application. If a parent property is specified, its properties will be copied into the BrowserInfo object.

performSearch() implements the rules for matching a browser USER-AGENT string against the patterns specified in browscap.ini: first check for an exact match; if there is none, return the pattern that has the smallest number of characters matching wildcards:

private BrowserPattern performSearch(String userAgent) {

We start by iterating through the BrowserPatterns, checking for an exact match. If we find one, we simply return it:

Iterator entries = browserMap.values().iterator();
while (entries.hasNext()) {
	BrowserPattern currentEntry = (BrowserPattern) entries.next();
	if (currentEntry.matchExact(userAgent)) {

		return currentEntry;
	}
}

If there was no exact match, we must instead look for the best match involving wildcards:

entries = browserMap.values().iterator();
BrowserPattern bestPattern = null;
int bestScore = BrowserPattern.NO_MATCH;

while (entries.hasNext()) {
	BrowserPattern currentEntry = (BrowserPattern) entries.next();

If a particular BrowserPattern doesn't have any wildcards, there's obviously no need to try:

if (!currentEntry.usesRE()) {
continue;
}

Otherwise, we check how good a match it was and compare with the previous known best match:

		int currentScore = currentEntry.matchRE(userAgent);
		if (currentScore < bestScore) {
			bestScore = currentScore;
			bestPattern = currentEntry;
		}
	}
	return bestPattern;
}

Finally, the lookup() method is used to convert an USER-AGENT into a BrowserInfo object. This is the method that our filter will call when a request comes in. Starting with the default browser properties, we first check to see whether it has a parent property and if so add the parent's properties, then add the properties of the BrowserPattern that matches best:

protected BrowserInfo lookup(String userAgent) {

Load the default browser properties:

BrowserInfo theBrowser =
	new BrowserInfo(defaultBrowserPattern.getProperties());

We need to check just in case someone fails to give us a USER-AGENT at all – in that case, we simply return the default settings:

if (userAgent == null) {
	return theBrowser;
}

For completeness, we store the USER-AGENT string in the BrowserInfo object:

theBrowser.addProperty("useragent", userAgent);

Next, we invoke performSearch() to try to match the USER-AGENT:

BrowserPattern thePattern = performSearch(userAgent);

If we didn't find anything we just return the defaults:

if (thePattern == null) {
	return theBrowser;
}

If we have a parent entry, add its properties:

String parentName = thePattern.getProperty("parent");
if (parentName != null) {
	BrowserPattern parentEntry =
		(BrowserPattern) browserMap.get(parentName);
	theBrowser.addProperties(parentEntry.getProperties());
}

Finally, we add our specific properties to the BrowserInfo object and return it:

		theBrowser.addProperties(thePattern.getProperties());
		return theBrowser;
	}
}

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