Saturday, May 31, 2008

Access Windows Registry using 'pure' Java

(rehash of my old post since all those wonderful blog post drafts I was planning to publish are unfortunately out-dated or irrelevant)

One can use the private code of Sun's Preferences API to access values of type REG_SZ in the Windows Registry. Stupid hack. Maybe I should make a library out of this. I have used this soooo many times.

The java.util.prefs.WindowsPreferences is the concrete implementation of AbstractPreferences in the Windows platform. This class provides methods like WindowsRegQueryValueEx, etc. Using Reflection, one can use the methods in this class to query string values under HKEY_LOCAL_MACHINE and HKEY_CURRENT_USER

Given below is a code-snippet that demonstrates how to get the ProxyServer setting on Windows (this is what IE uses/sets) and the Internet Explorer version

import java.lang.reflect.Method;
import java.util.prefs.Preferences;

public class JavaRegistryHack {

private static final int HKEY_CURRENT_USER = 0x80000001;
private static final int KEY_QUERY_VALUE = 1;
private static final int KEY_SET_VALUE = 2;
private static final int KEY_READ = 0x20019;

public static void main(String args[]) {
final Preferences userRoot = Preferences.userRoot();
final Preferences systemRoot = Preferences.systemRoot();
final Class clz = userRoot.getClass();
try {
final Method openKey = clz.getDeclaredMethod("openKey",
byte[].class, int.class, int.class);

final Method closeKey = clz.getDeclaredMethod("closeKey",

final Method winRegQueryValue = clz.getDeclaredMethod(
"WindowsRegQueryValueEx", int.class, byte[].class);
final Method winRegEnumValue = clz.getDeclaredMethod(
"WindowsRegEnumValue1", int.class, int.class, int.class);
final Method winRegQueryInfo = clz.getDeclaredMethod(
"WindowsRegQueryInfoKey1", int.class);

byte[] valb = null;
String vals = null;
String key = null;
Integer handle = -1;

//Query Internet Settings for Proxy
key = "Software\\Microsoft\\Windows\\CurrentVersion\\Internet Settings";
handle = (Integer) openKey.invoke(userRoot, toCstr(key), KEY_READ, KEY_READ);
valb = (byte[]) winRegQueryValue.invoke(userRoot, handle.intValue(),
vals = (valb != null ? new String(valb).trim() : null);
System.out.println("Proxy Server = " + vals);
closeKey.invoke(Preferences.userRoot(), handle);

// Query for IE version
key = "SOFTWARE\\Microsoft\\Internet Explorer";
handle = (Integer) openKey.invoke(systemRoot, toCstr(key), KEY_READ, KEY_READ);
valb = (byte[]) winRegQueryValue.invoke(systemRoot, handle, toCstr("Version"));
vals = (valb != null ? new String(valb).trim() : null);
System.out.println("Internet Explorer Version = " + vals);
closeKey.invoke(Preferences.systemRoot(), handle);

} catch (Exception e) {

private static byte[] toCstr(String str) {
byte[] result = new byte[str.length() + 1];
for (int i = 0; i < str.length(); i++) {
result[i] = (byte) str.charAt(i);
result[str.length()] = 0;
return result;

Google Collections now in Maven repository

(This blog has been dead for like forever - so many draft entries that were never turned to posts over the last year, but *shrug*)

Google Collections has now been mavenized, or to be more precise - the artifacts are present in the maven repository. Check out Maven Repo1 and the issue that reports this.

Just add the below to your &lt;project&amp;gt;.pom and you are good to go.


(Google collection's is like the Apache commons collections but generified)