[Java] 既に存在する名前だったら末尾に連番を付加

UniqueName.java

public String toUniqueName(String srcName, final List<String> existing) {
  return toUniqueName(srcName, "", new NameChecker() {
    @Override
    public boolean exists(String name) {
      return existing.contains(name);
    }
  });
}

public File toUniqueFile(File file) {
  String basePath = file.getParent() + File.separator
      + getBaseName(file.getName());
  String extension = getExtension(file.getName());

  String suffix = "";
  if (!"".equals(extension)) {
    suffix = "." + extension;
  }

  String uniquePath = toUniqueName(basePath, suffix, new NameChecker() {
    @Override
    public boolean exists(String name) {
      return new File(name).exists();
    }
  });

  return new File(uniquePath);
}

private String toUniqueName(String srcName, String suffix, NameChecker checker) {
  String retName = srcName + suffix;
  for (int i = 2; checker.exists(retName); i++) {
    retName = srcName + "(" + i + ")" + suffix;
  }
  return retName;
}

private interface NameChecker {
  boolean exists(String name);
}

private String getBaseName(String fileName) {
  int dotIdx = fileName.lastIndexOf('.');
  if (dotIdx < 0) {
    return fileName;
  }
  return fileName.substring(0, dotIdx);
}

private String getExtension(String fileName) {
  int dotIdx = fileName.lastIndexOf('.');
  if (dotIdx < 0) {
    return "";
  }
  return fileName.substring(dotIdx + 1, fileName.length());
}

@Test
public void testToUniqueName() {
  List<String> names = Arrays.asList("nameA", "nameB", "nameB(2)");
  assertEquals("nameA(2)", toUniqueName("nameA", names));
  assertEquals("nameB(3)", toUniqueName("nameB", names));
  assertEquals("nameC", toUniqueName("nameC", names));
}

@Test
public void testToUniqueFile() throws IOException {
  final String baseName = System.getProperty("java.io.tmpdir") + "testfile";
  final String suffix = ".csv";
  File file = new File(baseName + suffix);

  File file1 = toUniqueFile(file);
  assertEquals(baseName + suffix, file1.getPath());

  file1.createNewFile();
  file1.deleteOnExit();
  File file2 = toUniqueFile(file);
  assertEquals(baseName + "(2)" + suffix, file2.getPath());

  file2.createNewFile();
  file2.deleteOnExit();
  File file3 = toUniqueFile(file);
  assertEquals(baseName + "(3)" + suffix, file3.getPath());
}

@Test
public void testToUniqueFileNoExt() throws IOException {
  final String baseName = System.getProperty("java.io.tmpdir") + "testnoext";
  File file = new File(baseName);

  File file1 = toUniqueFile(file);
  assertEquals(baseName, file1.getPath());

  file1.createNewFile();
  file1.deleteOnExit();
  File file2 = toUniqueFile(file);
  assertEquals(baseName + "(2)", file2.getPath());
}

ファイル拡張子に対応、ファイル以外にもListに対応して汎用化