InputStream 與OutputStream是字節流中的輸入流和輸出流。

public class FileStream {

    public static void main(String[] args) {
        FileStream fs = new FileStream();
        // String content =
        // fs.readFileWithInputStream("/home/rding/file/File1.txt");
        // System.out.println(content);

        fs.writeFileWithOutputStream(
 
"/home/rding/file/File3.txt", "Hello File3");

        // fs.copyFile("/home/rding/file/File3.txt",
        // "/home/rding/file/File4.txt");

    }

    public void copyFile(String srcPath, String descPath) {
        InputStream inStream = null;
        OutputStream outStream = null;
        try {
            inStream 
 
= new FileInputStream(srcPath);
            outStream = new FileOutputStream(descPath);
            int size = inStream.available();
            byte[] byteArr = new byte[size];
            inStream.read(byteArr);
            outStream.write(byteArr);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } 
 
catch (IOException e) {
            e.printStackTrace();
        }

    }

    public void writeFileWithOutputStream(String filePath, String content) {
        OutputStream outStream = null;
        byte[] byteArr = content.getBytes();
        try {
　　　　　　　 //註意，outStream第一次建立後，就不會更新了，必須關閉再重新建立
            outStream = new FileOutputStream(filePath);
            // outStream = new FileOutputStream(new File(filePath));
　　　　　　　//  如果傳入參數true，則接著原來文件後面繼續寫，而不是覆蓋源文件。
            // outStream = new FileOutputStream(filePath, true);
            // outStream = new FileOutputStream(new File(filePath), true);

            outStream.write(byteArr);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (outStream != null) {
                try {
                    outStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    public String readFileWithInputStream(String filePath) {
        InputStream inStream = null;
        String result = "";
        try {
            inStream = new FileInputStream(filePath);
            // inStream = new FileInputStream(new File(filePath));
            int size = inStream.available();
            byte[] byteArr = new byte[size];
            inStream.read(byteArr);
            result = new String(byteArr);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inStream != null) {
                try {
                    inStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return result;
    }

}

Java文件流之字節流