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Query Windows registryTag(s): Environment


We launch the REG utility and capture the output. The performance is poor so it's a good idea to cache frequently used values.

Note : The Microsoft Windows NT Server 4.0 Resource Kit contains REG.EXE. In Windows 2000 and later REG.EXE is a native command. The REG utility can be used to write values in the registry (reg add /? for more infos).

In this example,we query the registry to extract the personal folder path ("My Documents") and the processor ID and its name.

import java.io.*;

public class RegQuery {

  private static final String REGQUERY_UTIL = "reg query ";
  private static final String REGSTR_TOKEN = "REG_SZ";
  private static final String REGDWORD_TOKEN = "REG_DWORD";

  private static final String PERSONAL_FOLDER_CMD = REGQUERY_UTIL +
    "\"HKCU\\Software\\Microsoft\\Windows\\CurrentVersion\\"
     + "Explorer\\Shell Folders\" /v Personal";
  private static final String CPU_SPEED_CMD = REGQUERY_UTIL +
    "\"HKLM\\HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0\""
     + " /v ~MHz";
  private static final String CPU_NAME_CMD = REGQUERY_UTIL +
   "\"HKLM\\HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0\""
     + " /v ProcessorNameString";

  public static String getCurrentUserPersonalFolderPath() {
    try {
      Process process = Runtime.getRuntime().exec(PERSONAL_FOLDER_CMD);
      StreamReader reader = new StreamReader(process.getInputStream());

      reader.start();
      process.waitFor();
      reader.join();

      String result = reader.getResult();
      int p = result.indexOf(REGSTR_TOKEN);

      if (p == -1)
         return null;

      return result.substring(p + REGSTR_TOKEN.length()).trim();
    }
    catch (Exception e) {
      return null;
    }
  }

  public static String getCPUSpeed() {
    try {
      Process process = Runtime.getRuntime().exec(CPU_SPEED_CMD);
      StreamReader reader = new StreamReader(process.getInputStream());

      reader.start();
      process.waitFor();
      reader.join();

      String result = reader.getResult();
      int p = result.indexOf(REGDWORD_TOKEN);

      if (p == -1)
         return null;

      // CPU speed in Mhz (minus 1) in HEX notation, convert it to DEC
      String temp = result.substring(p + REGDWORD_TOKEN.length()).trim();
      return Integer.toString
          ((Integer.parseInt(temp.substring("0x".length()), 16) + 1));
    }
    catch (Exception e) {
      return null;
    }
  }

  public static String getCPUName() {
    try {
      Process process = Runtime.getRuntime().exec(CPU_NAME_CMD);
      StreamReader reader = new StreamReader(process.getInputStream());

      reader.start();
      process.waitFor();
      reader.join();

      String result = reader.getResult();
      int p = result.indexOf(REGSTR_TOKEN);

      if (p == -1)
         return null;

      return result.substring(p + REGSTR_TOKEN.length()).trim();
    }
    catch (Exception e) {
      return null;
    }
  }

  static class StreamReader extends Thread {
    private InputStream is;
    private StringWriter sw;

    StreamReader(InputStream is) {
      this.is = is;
      sw = new StringWriter();
    }

    public void run() {
      try {
        int c;
        while ((c = is.read()) != -1)
          sw.write(c);
        }
        catch (IOException e) { ; }
      }

    String getResult() {
      return sw.toString();
    }
  }

  public static void main(String s[]) {
    System.out.println("Personal directory : "
       + getCurrentUserPersonalFolderPath());
    System.out.println("CPU Name : " + getCPUName());
    System.out.println("CPU Speed : " + getCPUSpeed() + " Mhz");
  }
}

See also this HowTo and this one.

For a better way to access the Registry, see Read/Write Windows Registry using JNA.


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