Developers, Developers, Developers! Maksim Sorokin IT Blog

Working with Windows Registry in Java 2

Ok, so the way to read registry data, which I described in previous post may be not a good idea. It is safer to rely on Windows Reg command. I wrote a simple utility to query registry using that utility.

• isExists finds whereas registry path exists
• get gets the value for specific key on certain registry path

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

public class WindowsRegistry {

  public static boolean isExists(WindowsRegistryRootKey rootKey, String registryPath) throws Exception {
    return (getOutput(rootKey, registryPath).size() > 0);
  }

  public static String get(WindowsRegistryRootKey rootKey, String registryPath, String key) throws Exception {
    List output = getOutput(rootKey, registryPath, key);

    return (getValueFromOutput(output));
  }

  static List getOutput(WindowsRegistryRootKey rootKey, String registryPath) throws Exception {
    if ((rootKey == null) || (registryPath == null)) {
      return new ArrayList();
    }

    String command = String.format("reg query \"%s\\%s\"", rootKey.getRootKey(), registryPath);

    return execRegQuery(command);
  }

  public static List getOutput(WindowsRegistryRootKey rootKey, String registryPath, String key) throws Exception {
    if ((rootKey == null) || (registryPath == null) || (key == null)) {
      return new ArrayList();
    }

    String command = String.format("reg query \"%s\\%s\" /v %s", rootKey.getRootKey(), registryPath, key);

    return execRegQuery(command);
  }

  private static List execRegQuery(String command) throws Exception {
    List result = new ArrayList();

    Process process = Runtime.getRuntime().exec(command);

    InputStreamReader isr = new InputStreamReader(process.getInputStream());
    BufferedReader br = new BufferedReader(isr);
    String line;
    while ((line = br.readLine()) != null) {
      result.add(line);
    }

    return result;
  }

  static String getValueFromOutput(List output) {
    for (String line : output) {
      String[] chunks = line.split("    ");
      if (isChunksValid(chunks)) {
        return chunks[3];
      }
    }

    return null;
  }

  private static boolean isChunksValid(String[] chunks) {
    if ((chunks.length != 4) || (chunks[0].trim().length() != 0)) {
      return false;
    }

    for (int i = 1; i < chunks.length; i++) {
      String chunk = chunks[i];
      if (chunk.trim().length() == 0) {
        return false;
      }
    }

    return true;
  }
}

public enum WindowsRegistryRootKey {

  HKEY_LOCAL_MACHINE("HKLM");

  private String rootKey;

  WindowsRegistryRootKey(String rootKey) {
    this.rootKey = rootKey;
  }

  String getRootKey() {
    return rootKey;
  }
}

And tests!

import java.util.ArrayList;
import java.util.List;

import org.junit.Assert;
import org.junit.Test;

public class WindowsRegistryTest {

  @Test
  public void testIsExists_doesntExist() throws Exception {
    Assert.assertFalse(WindowsRegistry.isExists(WindowsRegistryRootKey.HKEY_LOCAL_MACHINE, "a"));
  }

  @Test
  public void testIsExists() throws Exception {
    Assert.assertTrue(WindowsRegistry.isExists(WindowsRegistryRootKey.HKEY_LOCAL_MACHINE, "SOFTWARE\\Microsoft\\Windows\\CurrentVersion"));
  }

  @Test
  public void testGetOutput_passNull1() throws Exception {
    Assert.assertEquals(0, WindowsRegistry.getOutput(null, "a").size());
  }

  @Test
  public void testGetOutput_passNull2() throws Exception {
    Assert.assertEquals(0, WindowsRegistry.getOutput(WindowsRegistryRootKey.HKEY_LOCAL_MACHINE, null).size());
  }

  @Test
  public void testGetOutput_passNullBoth() throws Exception {
    Assert.assertEquals(0, WindowsRegistry.getOutput(null, null).size());
  }

  @Test
  public void testGetOutput2_passNull1() throws Exception {
    Assert.assertEquals(0, WindowsRegistry.getOutput(null, "a", "b").size());
  }

  @Test
  public void testGetOutput2_passNull2() throws Exception {
    Assert.assertEquals(0, WindowsRegistry.getOutput(WindowsRegistryRootKey.HKEY_LOCAL_MACHINE, "a", null).size());
  }

  @Test
  public void testGetOutput2_passNull3() throws Exception {
    Assert.assertEquals(0, WindowsRegistry.getOutput(WindowsRegistryRootKey.HKEY_LOCAL_MACHINE, null, "b").size());
  }

  @Test
  public void testGetOutput2_passNullAll() throws Exception {
    Assert.assertEquals(0, WindowsRegistry.getOutput(null, null, null).size());
  }

  @Test
  public void testGetValueFromOutput_noValid() throws Exception {
    List output = new ArrayList();
    output.add("HKEY");

    Assert.assertNull(WindowsRegistry.getValueFromOutput(output));
  }

  @Test
  public void testGetValueFromOutput() throws Exception {
    List output = new ArrayList();
    output.add("                              ");
    output.add("HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion");
    output.add("    ProductName    REG_SZ    Windows 7 Professional");

    Assert.assertEquals("Windows 7 Professional", WindowsRegistry.getValueFromOutput(output));
  }
}