java如何高效的读取超长字符串？

Question

字符串大概有1~2mb,每次读取都要1s多,如何进行优化？根据以下方法，为什么nio比io还慢？哪里写的有问题？//普通IO耗时1.3s    public static String openStringFileIO(String path, String fileName) {        long time = System.currentTimeMillis();        String result = null;        File f = new File(path, fileName);        try {            FileInputStream fileInputStream = new FileInputStream(f);            StringBuilder buffer = new StringBuilder();            String line;            BufferedReader in = new BufferedReader(new InputStreamReader(fileInputStream));            while ((line = in.readLine()) != null) {                buffer.append(line);            }            result = buffer.toString();        } catch (IOException e) {            e.printStackTrace();        }        Logger.d("openStringFileIO " + (System.currentTimeMillis() - time));        return result;    }    //NIO耗时 2.5s    public static String openStringFileNIO(String path, String fileName) {        long time = System.currentTimeMillis();        FileInputStream in = null;        StringBuilder result = new StringBuilder();        try {            File f = new File(path, fileName);            in = new FileInputStream(f);            FileChannel fc = in.getChannel();            ByteBuffer byteBuffer = ByteBuffer.allocate(1024); // 定义字节缓冲区            CharBuffer charBuffer = CharBuffer.allocate(1024); // 定义解码后字符存储缓冲区            CharsetDecoder decoder = Charset.forName("UTF-8").newDecoder();// 定义合适的字符集解码器            while ((fc.read(byteBuffer)) != -1) { // 读取字符串到缓冲区                byteBuffer.flip();                charBuffer.clear();                // 对byteBuffer进行解码                if (fc.position() < fc.size()) {                    decoder.decode(byteBuffer, charBuffer, false);                } else {                    // 最后一次解码                    decoder.decode(byteBuffer, charBuffer, true);                    decoder.flush(charBuffer);                }                byteBuffer.compact(); // 注意此处调用compact方法，而不是clear方法                charBuffer.flip();

Answer 1

new StringBuilder(1000000)这里写大点，最好可以预估你要存的字符串的长度，减少扩容可以提升时间

Answer 2

1. 建议尝试OKIO,guava或者apache下的comons

Answer 3

1.可以把文件切成几块，然后通过多线程读取
2.可以使用RandomAccessFile配合多线程来操作