java基础读取

public static void stream() { String fileName = "D:\test.txt"; final String CHARSET_NAME = "UTF-8"; List<String> 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()); }

public static void nioOfJDK7() { String fileName = "D:\test.txt"; final String CHARSET_NAME = "UTF-8"; List<String> 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()); }

public static void streamOfJDK7() { String fileName = "D:\test.txt"; final String CHARSET_NAME = "UTF-8"; List<String> 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()); }

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<String> 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 < readSize && readByte[i + 1] == ASCII_CR) { startNum = i + 2; } else { startNum = i + 1; } } } if (hasLF) { temp = new byte[readByte.length - startNum]; System.arraycopy(readByte, startNum, temp, 0, temp.length); } else { // 单次读取的内容不足一行的情况 byte[] toTemp = new byte[temp.length + readByte.length]; System.arraycopy(temp, 0, toTemp, 0, temp.length); System.arraycopy(readByte, 0, toTemp, temp.length, readByte.length); temp = toTemp; } } // 最后一行 if (temp.length > 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()); }

<dependency> <groupId>commons-io</groupId> <artifactId>commons-io</artifactId> <version>2.11.0</version> </dependency>

public static void fileOfCommonsIO() { String fileName = "D:\test.txt"; final String CHARSET_NAME = "UTF-8"; List<String> 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()); }

<dependency> <groupId>commons-io</groupId> <artifactId>commons-io</artifactId> <version>2.11.0</version> </dependency>

public static void ioOfCommonsIO() { String fileName = "D:\test.txt"; final String CHARSET_NAME = "UTF-8"; List<String> 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()); }

<dependency> <groupId>cn.hutool</groupId> <artifactId>hutool-core</artifactId> <version>5.8.10</version> </dependency> 或者： <dependency> <groupId>cn.hutool</groupId> <artifactId>hutool-all</artifactId> <version>5.8.10</version> </dependency>

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

<dependency> <groupId>cn.hutool</groupId> <artifactId>hutool-core</artifactId> <version>5.8.10</version> </dependency> 或者： <dependency> <groupId>cn.hutool</groupId> <artifactId>hutool-all</artifactId> <version>5.8.10</version> </dependency>

public static void ioOfHutool() { String fileName = "D:\test.txt"; final String CHARSET_NAME = "UTF-8"; List<String> 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()); }

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()); }