InputStreamReader是Java中用于從InputStream讀取數據的類，它將字節流轉換為字符流。它有以下主要的用法：

1. 從InputStream中讀取數據，并將其轉換為字符流：

InputStream inputStream = new FileInputStream("file.txt");
Reader reader = new InputStreamReader(inputStream);
int data = reader.read();
while (data != -1) {
    System.out.print((char) data);
    data = reader.read();
}
reader.close();

2. 指定字符編碼格式：

InputStream inputStream = new FileInputStream("file.txt");
Reader reader = new InputStreamReader(inputStream, "UTF-8");

3. 使用BufferedReader包裝InputStreamReader，以提高讀取性能：

InputStream inputStream = new FileInputStream("file.txt");
Reader reader = new InputStreamReader(inputStream);
BufferedReader bufferedReader = new BufferedReader(reader);
String line = bufferedReader.readLine();
while (line != null) {
    System.out.println(line);
    line = bufferedReader.readLine();
}
bufferedReader.close();

4. 使用try-with-resources來自動關閉流：

try (InputStream inputStream = new FileInputStream("file.txt");
     Reader reader = new InputStreamReader(inputStream)) {
    int data = reader.read();
    while (data != -1) {
        System.out.print((char) data);
        data = reader.read();
    }
} catch (IOException e) {
    e.printStackTrace();
}