浅谈Java几种文件读取方式耗时

2023-05-15 17:08

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BufferedReader

代码：

    public static String ReadFileByBufferReaderToString(String path) {
        if (TextUtils.isEmpty(path)) {
            return "";
        }
        StringBuilder stringBuilder = new StringBuilder();
        try (BufferedReader bufferedReader = new BufferedReader(new FileReader(path))) {
            String tempStr;
            while ((tempStr = bufferedReader.readLine()) != null) {
                stringBuilder.append(tempStr).append(System.lineSeparator());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return stringBuilder.toString();
    }

这里我们使用stringbuilder去存储读取出来的字符串，加日志查看耗时，读取一个

onClick: readFileByBufferReaderStringBuilder tims use is 86

这里将文件读取出来之后存储方式改下，每次创建新的String字符串，测试一下每次创建新的字符串和使用StringBuilder之间的性能差异：

    public static String ReadFileByBufferReaderToStringUseString(String path) {
        if (TextUtils.isEmpty(path)) {
            return "";
        }
        String result = "";
        try (BufferedReader bufferedReader = new BufferedReader(new FileReader(path))) {
            String tempStr;
            while ((tempStr = bufferedReader.readLine()) != null) {
                result += tempStr;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        Log.i(TAG, "ReadFileToString: read success ");
        return result;
    }

2023-04-08 23:06:06.141 18416-18518/com.example.androidstart I/TestFileReadSpeed: onClick: readFileByBufferReaderString tims use is 264041

花了264041 ms，可见多次创建String对象对性能消耗非常大，所以字符串拼接的时候一定要使用StringBuilder，不能使用String直接相加

Files.readAllBytes

    @RequiresApi(api = Build.VERSION_CODES.O)
    public static String ReadFileByReadAllBytesReaderToString(String path) {
        if (TextUtils.isEmpty(path)) {
            return "";
        }
        String result = null;
        try {
            result = new String(Files.readAllBytes(Paths.get(path)));
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }

2023-04-09 17:38:06.989 7078-7359/com.example.androidstart I/TestFileReadSpeed: onClick: ReadFileByReadAllBytesReaderToString tims use is 68

耗时68ms，比上面的BufferReader行一行读取会快一些，但是这个API有一些限制就是必须在AndroidO及以上版本才可以使用。

Files.lines

    @RequiresApi(api = Build.VERSION_CODES.O)
    public static String ReadFileByByFilesReadLinesToString(String path) {
        if(TextUtils.isEmpty(path)){
            return "";
        }
        StringBuilder stringBuilder = new StringBuilder();
        try (Stream<String> stream = Files.lines(Paths.get(path))) {
            stream.forEach(new Consumer<String>() {
                @Override
                public void accept(String s) {
                    stringBuilder.append(s);
                }
            });
        } catch (IOException e) {
            e.printStackTrace();
        }
        return stringBuilder.toString();
    }

2023-04-09 17:46:14.342 7078-7078/com.example.androidstart I/TestFileReadSpeed: onClick: ReadFileByByFilesReadLinesToString tims use is 102

Files.lines耗时中等在100ms左右。

CommonIO::readFileToString

代码：

   public static String ReadFileByCommonIOReadFileToString(String path) {
        if (TextUtils.isEmpty(path)) {
            return "";
        }
        try {
            return FileUtils.readFileToString(new File(path), Charset.defaultCharset());
        } catch (IOException e) {
            e.printStackTrace();
        }
        return "";
    }