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Read/Write the Registry (Windows)Tag(s): Environment


The JDK contains the required code (java.util.prefs.WindowsPreferences) to access the Windows registry but to preserve the "purity" of Java, the code is declared as private so it's not visible. The trick is to use reflection to access private methods defined in the WindowsPreference class.

This technique was first seen in this post.

Remember : This code is a hack and may break anytime. A better alternative is to use JNA.

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 count = info[0];    // bug fix 20130112
    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 count = info[0];    // bug fix 20130112
    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);


      /*
         this code is broken under win7 64 :-(  20130112

      // 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\\Wow6432Node\\JavaSoft\\Java Runtime Environment");
      System.out.println("1:" + res1.toString());
      */

	  // on 64bit Windows, you need Wow6432Node to access 32bit related information
	  //   "SOFTWARE\\Wow6432Node\\Microsoft\\Windows NT\\CurrentVersion"
      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\Réal\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.


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Written and compiled by Réal Gagnon ©1998-2014
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