Java读取文件的几种方式

1. 使用流读取文件

public static void stream() {String fileName = "D:\\test.txt";final String CHARSET_NAME = "UTF-8";List content = new ArrayList();try (BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(fileName), CHARSET_NAME))) {String line;while ((line = br.readLine()) != null) {content.add(line);}} catch (Exception e) {e.printStackTrace();}//content.forEach(System.out::println);System.out.println(content.size());}

2. 使用JDK1.7提供的NIO读取文件(适用于小文件)

public static void nioOfJDK7() {String fileName = "D:\\test.txt";final String CHARSET_NAME = "UTF-8";List content = new ArrayList(0);try {content = Files.readAllLines(Paths.get(fileName), Charset.forName(CHARSET_NAME));} catch (Exception e) {e.printStackTrace();}//content.forEach(System.out::println);System.out.println(content.size());}

3. 使用JDK1.7提供的NIO读取文件(适用于大文件)

public static void streamOfJDK7() {String fileName = "D:\\test.txt";final String CHARSET_NAME = "UTF-8";List content = new ArrayList();try (BufferedReader br = Files.newBufferedReader(Paths.get(fileName), Charset.forName(CHARSET_NAME))) {String line;while ((line = br.readLine()) != null) {content.add(line);}} catch (Exception e) {e.printStackTrace();}//content.forEach(System.out::println);System.out.println(content.size());}

4. 使用JDK1.4提供的NIO读取文件(适用于超大文件)

public static void nioOfJDK4() {String fileName = "D:\\test.txt";final String CHARSET_NAME = "UTF-8";final int ASCII_LF = 10; // 换行符final int ASCII_CR = 13; // 回车符List content = new ArrayList();try (FileChannel fileChannel = new RandomAccessFile(fileName, "r").getChannel()) {ByteBuffer byteBuffer = ByteBuffer.allocate(1024 * 100);byte[] lineByte;byte[] temp = new byte[0];while (fileChannel.read(byteBuffer) != -1) {// 获取缓冲区位置，即读取长度int readSize = byteBuffer.position();// 将读取位置置0，并将读取位置标为废弃byteBuffer.rewind();// 读取内容byte[] readByte = new byte[readSize];byteBuffer.get(readByte);// 清除缓存区byteBuffer.clear();// 读取内容是否包含一整行boolean hasLF = false;int startNum = 0;for (int i = 0; i < readSize; i++) {if (readByte[i] == ASCII_LF) {hasLF = true;int tempNum = temp.length;int lineNum = i - startNum;// 数组大小已经去掉换行符lineByte = new byte[tempNum + lineNum];System.arraycopy(temp, 0, lineByte, 0, tempNum);temp = new byte[0];System.arraycopy(readByte, startNum, lineByte, tempNum, lineNum);String line = new String(lineByte, 0, lineByte.length, CHARSET_NAME);content.add(line);// 过滤回车符和换行符if (i + 1  0) {String lastLine = new String(temp, 0, temp.length, CHARSET_NAME);content.add(lastLine);}} catch (Exception e) {e.printStackTrace();}//content.forEach(System.out::println);System.out.println(content.size());}

5. 使用cmmons-io依赖提供的FileUtils工具类读取文件

添加依赖：

commons-iocommons-io2.11.0

public static void fileOfCommonsIO() {String fileName = "D:\\test.txt";final String CHARSET_NAME = "UTF-8";List content = new ArrayList(0);try {content = FileUtils.readLines(new File(fileName), CHARSET_NAME);} catch (Exception e) {e.printStackTrace();}//content.forEach(System.out::println);System.out.println(content.size());}

6. 使用cmmons-io依赖提供的IOtils工具类读取文件

添加依赖：

commons-iocommons-io2.11.0

public static void ioOfCommonsIO() {String fileName = "D:\\test.txt";final String CHARSET_NAME = "UTF-8";List content = new ArrayList(0);try {content = IOUtils.readLines(new FileInputStream(fileName), CHARSET_NAME);} catch (Exception e) {e.printStackTrace();}//content.forEach(System.out::println);System.out.println(content.size());}

7. 使用hutool依赖提供的FileUtil工具类读取文件

添加依赖：

cn.hutoolhutool-core5.8.10或者：cn.hutoolhutool-all5.8.10

public static void fileOfHutool() {String fileName = "D:\\test.txt";final String CHARSET_NAME = "UTF-8";List content = FileUtil.readLines(fileName, CHARSET_NAME);//content.forEach(System.out::println);System.out.println(content.size());}

8. 使用hutool依赖提供的IoUtil工具类读取文件

添加依赖：

cn.hutoolhutool-core5.8.10或者：cn.hutoolhutool-all5.8.10

public static void ioOfHutool() {String fileName = "D:\\test.txt";final String CHARSET_NAME = "UTF-8";List content = new ArrayList();try {IoUtil.readLines(new FileInputStream(fileName), CharsetUtil.charset(CHARSET_NAME), content);} catch (Exception e) {e.printStackTrace();}//content.forEach(System.out::println);System.out.println(content.size());}

9. 测试耗时

测试文件：30000行、21.8 MB

public static void main(String[] args) {StopWatch stopWatch = new StopWatch();stopWatch.start("stream");stream();stopWatch.stop();stopWatch.start("nioOfJDK7");nioOfJDK7();stopWatch.stop();stopWatch.start("streamOfJDK7");streamOfJDK7();stopWatch.stop();stopWatch.start("nioOfJDK4");nioOfJDK4();stopWatch.stop();stopWatch.start("fileOfCommonsIO");fileOfCommonsIO();stopWatch.stop();stopWatch.start("ioOfCommonsIO");ioOfCommonsIO();stopWatch.stop();stopWatch.start("fileOfHutool");fileOfHutool();stopWatch.stop();stopWatch.start("ioOfHutool");ioOfHutool();stopWatch.stop();for (StopWatch.TaskInfo taskInfo : stopWatch.getTaskInfo()) {System.out.println(taskInfo.getTaskName() + " -> " + taskInfo.getTimeMillis() + " ms");}//System.out.println(stopWatch.prettyPrint());}

测试3次耗时统计(单位：ms)：

从测试结果来看，Hutool提供的IoUtil、commons-io提供的IoUtil以及JDK1.7提供的NIO基于流方式耗时更优，但测试还应参考内存占用情况，具体可自行测试。