Read/Write the Registry (Windows)

his technique was first seen in this post.

package com.rgagnon.howto;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
import java.util.ArrayList;
import java.util.List;
import java.util.prefs.Preferences;

public class WinRegistry {
// inspired by
// http://javabyexample.wisdomplug.com/java-concepts/34-core-java/62-java-registry-wrapper.html
// http://www.snipcode.org/java/1-java/23-java-class-for-accessing-reading-and-writing-from-windows-registry.html
// http://snipplr.com/view/6620/accessing-windows-registry-in-java/
public static final int HKEY_CURRENT_USER = 0x80000001;
public static final int HKEY_LOCAL_MACHINE = 0x80000002;
public static final int REG_SUCCESS = 0;
public static final int REG_NOTFOUND = 2;
public static final int REG_ACCESSDENIED = 5;

private static final int KEY_ALL_ACCESS = 0xf003f;
private static final int KEY_READ = 0x20019;
private static Preferences userRoot = Preferences.userRoot();
private static Preferences systemRoot = Preferences.systemRoot();
private static Class<? extends Preferences> userClass = userRoot.getClass();
private static Method regOpenKey = null;
private static Method regCloseKey = null;
private static Method regQueryValueEx = null;
private static Method regEnumValue = null;
private static Method regQueryInfoKey = null;
private static Method regEnumKeyEx = null;
private static Method regCreateKeyEx = null;
private static Method regSetValueEx = null;
private static Method regDeleteKey = null;
private static Method regDeleteValue = null;

static {
try {
regOpenKey = userClass.getDeclaredMethod("WindowsRegOpenKey",
new Class[] { int.class, byte[].class, int.class });
regOpenKey.setAccessible(true);
regCloseKey = userClass.getDeclaredMethod("WindowsRegCloseKey",
new Class[] { int.class });
regCloseKey.setAccessible(true);
regQueryValueEx = userClass.getDeclaredMethod("WindowsRegQueryValueEx",
new Class[] { int.class, byte[].class });
regQueryValueEx.setAccessible(true);
regEnumValue = userClass.getDeclaredMethod("WindowsRegEnumValue",
new Class[] { int.class, int.class, int.class });
regEnumValue.setAccessible(true);
regQueryInfoKey = userClass.getDeclaredMethod("WindowsRegQueryInfoKey1",
new Class[] { int.class });
regQueryInfoKey.setAccessible(true);
regEnumKeyEx = userClass.getDeclaredMethod(
"WindowsRegEnumKeyEx", new Class[] { int.class, int.class,
int.class });
regEnumKeyEx.setAccessible(true);
regCreateKeyEx = userClass.getDeclaredMethod(
"WindowsRegCreateKeyEx", new Class[] { int.class,
byte[].class });
regCreateKeyEx.setAccessible(true);
regSetValueEx = userClass.getDeclaredMethod(
"WindowsRegSetValueEx", new Class[] { int.class,
byte[].class, byte[].class });
regSetValueEx.setAccessible(true);
regDeleteValue = userClass.getDeclaredMethod(
"WindowsRegDeleteValue", new Class[] { int.class,
byte[].class });
regDeleteValue.setAccessible(true);
regDeleteKey = userClass.getDeclaredMethod(
"WindowsRegDeleteKey", new Class[] { int.class,
byte[].class });
regDeleteKey.setAccessible(true);
}
catch (Exception e) {
e.printStackTrace();
}
}

private WinRegistry() { }

/**
* Read a value from key and value name
* @param hkey HKEY_CURRENT_USER/HKEY_LOCAL_MACHINE
* @param key
* @param valueName
* @return the value
* @throws IllegalArgumentException
* @throws IllegalAccessException
* @throws InvocationTargetException
*/
public static String readString(int hkey, String key, String valueName)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
if (hkey == HKEY_LOCAL_MACHINE) {
return readString(systemRoot, hkey, key, valueName);
}
else if (hkey == HKEY_CURRENT_USER) {
return readString(userRoot, hkey, key, valueName);
}
else {
throw new IllegalArgumentException("hkey=" + hkey);
}
}

/**
* Read value(s) and value name(s) form given key
* @param hkey HKEY_CURRENT_USER/HKEY_LOCAL_MACHINE
* @param key
* @return the value name(s) plus the value(s)
* @throws IllegalArgumentException
* @throws IllegalAccessException
* @throws InvocationTargetException
*/
public static Map<String, String> readStringValues(int hkey, String key)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
if (hkey == HKEY_LOCAL_MACHINE) {
return readStringValues(systemRoot, hkey, key);
}
else if (hkey == HKEY_CURRENT_USER) {
return readStringValues(userRoot, hkey, key);
}
else {
throw new IllegalArgumentException("hkey=" + hkey);
}
}

/**
* Read the value name(s) from a given key
* @param hkey HKEY_CURRENT_USER/HKEY_LOCAL_MACHINE
* @param key
* @return the value name(s)
* @throws IllegalArgumentException
* @throws IllegalAccessException
* @throws InvocationTargetException
*/
public static List<String> readStringSubKeys(int hkey, String key)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
if (hkey == HKEY_LOCAL_MACHINE) {
return readStringSubKeys(systemRoot, hkey, key);
}
else if (hkey == HKEY_CURRENT_USER) {
return readStringSubKeys(userRoot, hkey, key);
}
else {
throw new IllegalArgumentException("hkey=" + hkey);
}
}

/**
* Create a key
* @param hkey HKEY_CURRENT_USER/HKEY_LOCAL_MACHINE
* @param key
* @throws IllegalArgumentException
* @throws IllegalAccessException
* @throws InvocationTargetException
*/
public static void createKey(int hkey, String key)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
int [] ret;
if (hkey == HKEY_LOCAL_MACHINE) {
ret = createKey(systemRoot, hkey, key);
regCloseKey.invoke(systemRoot, new Object[] { new Integer(ret[0]) });
}
else if (hkey == HKEY_CURRENT_USER) {
ret = createKey(userRoot, hkey, key);
regCloseKey.invoke(userRoot, new Object[] { new Integer(ret[0]) });
}
else {
throw new IllegalArgumentException("hkey=" + hkey);
}
if (ret[1] != REG_SUCCESS) {
throw new IllegalArgumentException("rc=" + ret[1] + " key=" + key);
}
}

/**
* Write a value in a given key/value name
* @param hkey
* @param key
* @param valueName
* @param value
* @throws IllegalArgumentException
* @throws IllegalAccessException
* @throws InvocationTargetException
*/
public static void writeStringValue
(int hkey, String key, String valueName, String value)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
if (hkey == HKEY_LOCAL_MACHINE) {
writeStringValue(systemRoot, hkey, key, valueName, value);
}
else if (hkey == HKEY_CURRENT_USER) {
writeStringValue(userRoot, hkey, key, valueName, value);
}
else {
throw new IllegalArgumentException("hkey=" + hkey);
}
}

/**
* Delete a given key
* @param hkey
* @param key
* @throws IllegalArgumentException
* @throws IllegalAccessException
* @throws InvocationTargetException
*/
public static void deleteKey(int hkey, String key)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
int rc = -1;
if (hkey == HKEY_LOCAL_MACHINE) {
rc = deleteKey(systemRoot, hkey, key);
}
else if (hkey == HKEY_CURRENT_USER) {
rc = deleteKey(userRoot, hkey, key);
}
if (rc != REG_SUCCESS) {
throw new IllegalArgumentException("rc=" + rc + " key=" + key);
}
}

/**
* delete a value from a given key/value name
* @param hkey
* @param key
* @param value
* @throws IllegalArgumentException
* @throws IllegalAccessException
* @throws InvocationTargetException
*/
public static void deleteValue(int hkey, String key, String value)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
int rc = -1;
if (hkey == HKEY_LOCAL_MACHINE) {
rc = deleteValue(systemRoot, hkey, key, value);
}
else if (hkey == HKEY_CURRENT_USER) {
rc = deleteValue(userRoot, hkey, key, value);
}
if (rc != REG_SUCCESS) {
throw new IllegalArgumentException("rc=" + rc + " key=" + key + " value=" + value);
}
}

// =====================

private static int deleteValue
(Preferences root, int hkey, String key, String value)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
int[] handles = (int[]) regOpenKey.invoke(root, new Object[] {
new Integer(hkey), toCstr(key), new Integer(KEY_ALL_ACCESS) });
if (handles[1] != REG_SUCCESS) {
return handles[1]; // can be REG_NOTFOUND, REG_ACCESSDENIED
}
int rc =((Integer) regDeleteValue.invoke(root,
new Object[] {
new Integer(handles[0]), toCstr(value)
})).intValue();
regCloseKey.invoke(root, new Object[] { new Integer(handles[0]) });
return rc;
}

private static int deleteKey(Preferences root, int hkey, String key)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
int rc =((Integer) regDeleteKey.invoke(root,
new Object[] { new Integer(hkey), toCstr(key) })).intValue();
return rc; // can REG_NOTFOUND, REG_ACCESSDENIED, REG_SUCCESS
}

private static String readString(Preferences root, int hkey, String key, String value)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
int[] handles = (int[]) regOpenKey.invoke(root, new Object[] {
new Integer(hkey), toCstr(key), new Integer(KEY_READ) });
if (handles[1] != REG_SUCCESS) {
return null;
}
byte[] valb = (byte[]) regQueryValueEx.invoke(root, new Object[] {
new Integer(handles[0]), toCstr(value) });
regCloseKey.invoke(root, new Object[] { new Integer(handles[0]) });
return (valb != null ? new String(valb).trim() : null);
}

private static Map<String,String> readStringValues
(Preferences root, int hkey, String key)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
HashMap<String, String> results = new HashMap<String,String>();
int[] handles = (int[]) regOpenKey.invoke(root, new Object[] {
new Integer(hkey), toCstr(key), new Integer(KEY_READ) });
if (handles[1] != REG_SUCCESS) {
return null;
}
int[] info = (int[]) regQueryInfoKey.invoke(root,
new Object[] { new Integer(handles[0]) });

int count = info[2]; // count
int maxlen = info[3]; // value length max
for(int index=0; index<count; index++) {
byte[] name = (byte[]) regEnumValue.invoke(root, new Object[] {
new Integer
(handles[0]), new Integer(index), new Integer(maxlen + 1)});
String value = readString(hkey, key, new String(name));
results.put(new String(name).trim(), value);
}
regCloseKey.invoke(root, new Object[] { new Integer(handles[0]) });
return results;
}

private static List<String> readStringSubKeys
(Preferences root, int hkey, String key)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
List<String> results = new ArrayList<String>();
int[] handles = (int[]) regOpenKey.invoke(root, new Object[] {
new Integer(hkey), toCstr(key), new Integer(KEY_READ)
});
if (handles[1] != REG_SUCCESS) {
return null;
}
int[] info = (int[]) regQueryInfoKey.invoke(root,
new Object[] { new Integer(handles[0]) });

int count = info[2]; // count
int maxlen = info[3]; // value length max
for(int index=0; index<count; index++) {
byte[] name = (byte[]) regEnumKeyEx.invoke(root, new Object[] {
new Integer
(handles[0]), new Integer(index), new Integer(maxlen + 1)
});
results.add(new String(name).trim());
}
regCloseKey.invoke(root, new Object[] { new Integer(handles[0]) });
return results;
}

private static int [] createKey(Preferences root, int hkey, String key)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
return (int[]) regCreateKeyEx.invoke(root,
new Object[] { new Integer(hkey), toCstr(key) });
}

private static void writeStringValue
(Preferences root, int hkey, String key, String valueName, String value)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException
{
int[] handles = (int[]) regOpenKey.invoke(root, new Object[] {
new Integer(hkey), toCstr(key), new Integer(KEY_ALL_ACCESS) });

regSetValueEx.invoke(root,
new Object[] {
new Integer(handles[0]), toCstr(valueName), toCstr(value)
});
regCloseKey.invoke(root, new Object[] { new Integer(handles[0]) });
}

// utility
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;
}
}

How to use it :

package com.rgagnon.howto;

public class WinRegistryTest {
public static void main(String args[]) throws Exception {
String value = "";

// IE Download directory (HKEY_CURRENT_USER)
value = WinRegistry.readString(
WinRegistry.HKEY_CURRENT_USER,
"Software\\Microsoft\\Internet Explorer",
"Download Directory");
System.out.println("IE Download directory = " + value);

// Query for Acrobat Reader installation path (HKEY_LOCAL_MACHINE)
value = WinRegistry.readString(
WinRegistry.HKEY_LOCAL_MACHINE,
"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\App Paths\\AcroRd32.exe",
"");
System.out.println("Acrobat Reader Path = " + value);

// Loop through installed JRE and print the JAVA_HOME value
// HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment
java.util.Map res1 = WinRegistry.readStringValues(
WinRegistry.HKEY_LOCAL_MACHINE,
"SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion");
System.out.println(res1.toString());

java.util.List res2 = WinRegistry.readStringSubKeys(
WinRegistry.HKEY_LOCAL_MACHINE,
"SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion");
System.out.println(res2.toString());

WinRegistry.createKey(
WinRegistry.HKEY_CURRENT_USER, "SOFTWARE\\rgagnon.com");
WinRegistry.writeStringValue(
WinRegistry.HKEY_CURRENT_USER,
"SOFTWARE\\rgagnon.com",
"HowTo",
"java");

// WinRegistry.deleteValue(
// WinRegistry.HKEY_CURRENT_USER,
// "SOFTWARE\\rgagnon.com", "HowTo");
// WinRegistry.deleteKey(
// WinRegistry.HKEY_CURRENT_USER,
// "SOFTWARE\\rgagnon.com\\");

System.out.println("Done." );
}
}


The output :

IE Download directory = C:\Documents and Settings\R閍l\Bureau
Acrobat Reader Path = C:\Program Files\Adobe\Acrobat 5.0\Reader\AcroRd32.exe
{SubVersionNumber=, CurrentBuild=1.511.1 () (snipped)...
[Accessibility, AeDebug, Asr, Classes, Compatibility, (snipped)...
Done.