java读取文件的几种方法

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1 使用FileInputStream

package file.io.readfile; import java.io.*; public class FileInputStreamTest { public static void main(String[] args) throws Exception { // testInputStream(); // testInputStream2(); testInputStream3(); // testInputStreamReader(); } public static void testInputStream() throws Exception { String path = "E:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; long length = new File(path).length(); byte[] buffer = new byte[(int)length]; FileInputStream fileInputStream = new FileInputStream(path); int unread = (int)length; // 如果是大文件，需要多次读，这里简单地一次读取文件全部内容 // 多次读取可以采用的方式: // 分配一个大内存，每次读取通过指定偏移以及读取数据大小来移动偏移 // 全部数据使用一个大内存，分配一个小内存来存储每次读取的数据，然后把每次读取的数据复制到大内存 try (BufferedInputStream bf = new BufferedInputStream(fileInputStream)) { bf.read(buffer, 0, unread); } System.out.println(new String(buffer)); } public static void testInputStream2() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; long length = new File(path).length(); byte[] buffer = new byte[(int)length]; FileInputStream fileInputStream = new FileInputStream(path); int unread = (int)length; // 如果是大文件，需要多次读，这里简单地一次读取文件全部内容 // 多次读取可以采用的方式: // 分配一个大内存，每次读取通过指定偏移以及读取数据大小来移动偏移 // 全部数据使用一个大内存，分配一个小内存来存储每次读取的数据，然后把每次读取的数据复制到大内存 int n; int pos = 0; try (BufferedInputStream bf = new BufferedInputStream(fileInputStream)) { while((n = bf.read(buffer, pos, unread)) > 0) { pos += n; unread = unread - n; } } System.out.println(new String(buffer)); } public static void testInputStream3() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; long length = new File(path).length(); byte[] buffer = new byte[(int)length]; FileInputStream fileInputStream = new FileInputStream(path); int unread = (int)length; // 如果是大文件，需要多次读，这里简单地一次读取文件全部内容 // 多次读取可以采用的方式: // 分配一个大内存，每次读取通过指定偏移以及读取数据大小来移动偏移 // 全部数据使用一个大内存，分配一个小内存来存储每次读取的数据，然后把每次读取的数据复制到大内存 int n; int pos = 0; byte[] readBuf = new byte[1024]; try (BufferedInputStream bf = new BufferedInputStream(fileInputStream)) { while((n = bf.read(readBuf)) > 0) { int size = Math.min(n, unread); System.arraycopy(readBuf, 0, buffer, pos, size); pos += n; unread = unread - n; // 考虑文件增大，比刚开始大小大的情况。 if (unread <= 0) { break; } } } System.out.println(new String(buffer)); } / * 使用字符流 * @throws Exception */ public static void testInputStreamReader() throws Exception { String path = "E:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; long length = new File(path).length(); byte[] buffer = new byte[(int)length]; FileInputStream fileInputStream = new FileInputStream(path); int unread = (int)length; // 按行读取，读到的每一行不包括末尾的换行符 try (BufferedReader bf = new BufferedReader(new InputStreamReader(fileInputStream))) { String line; while ((line = bf.readLine()) != null) { System.out.println(line); } } System.out.println(new String(buffer)); } } 

1.1 小结

2 使用FileReader

package file.io.readfile; import java.io.BufferedReader; import java.io.FileReader; public class FileReaderTest { public static void main(String[] args) throws Exception { testReader(); } public static void testReader() throws Exception { String path = "E:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; // 使用FileReader不能指定文件编码 try (BufferedReader bf = new BufferedReader(new FileReader(path))) { String line; while ((line = bf.readLine()) != null) { System.out.println(line); } } } } 

2.1 小结

字符流方式读取文件，适合按行读取情况。

3 使用RandomAccessFile

package file.io.readfile; import java.io.RandomAccessFile; / * @description: * @author: LiYuan * @date: 2024/7/24 9:51 */ public class RandomAccessFileTest { public static void main(String[] args) throws Exception { test1(); } public static void test1() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; try (RandomAccessFile randomAccessFile = new RandomAccessFile(path, "rw")) { // 获取文件大小 // 另一个获取文件大小的方法是new File(path).length() // 通过打开文件流来获取文件大小的方法更好，原因有： // 避免两次打开文件； // 避免并发问题导致获取文件大小错误 long length = randomAccessFile.length(); byte[] buffer = new byte[(int)length]; // 可以使用readLine分行读取 // 如果是大文件，需要多次读取 // 严格来说，需要判断是否读取完了整个文件 randomAccessFile.read(buffer); System.out.println(new String(buffer)); } } } 

3.1 小结

4 使用Scanner

package file.io.readfile; import java.io.FileReader; import java.util.Scanner; / * @description: * @author: LiYuan * @date: 2024/7/24 10:48 */ public class ScannerTest { public static void main(String[] args) throws Exception { // test1(); // test2(); // test3(); test4(); } public static void test1() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; try (Scanner scanner = new Scanner(new FileReader(path))) { // 按空格分隔 while (scanner.hasNext()) { String line = scanner.next(); System.out.println(line); } } } public static void test2() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; try (Scanner scanner = new Scanner(new FileReader(path))) { // 按空格分隔 while (scanner.hasNextLine()) { String line = scanner.nextLine(); System.out.println(line); } } } public static void test3() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; try (Scanner scanner = new Scanner(new FileReader(path))) { // 指定分隔符 scanner.useDelimiter("\n"); while (scanner.hasNext()) { String line = scanner.next(); System.out.println(line); } } } public static void test4() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; try (Scanner scanner = new Scanner(new FileReader(path))) { // 指定分隔符 scanner.useDelimiter(" "); while (scanner.hasNext()) { String word = scanner.next(); System.out.println(word); } } } } 

5 使用java.nio.file.Files

package file.io.readfile; import java.io.BufferedReader; import java.nio.charset.StandardCharsets; import java.nio.file.Files; import java.nio.file.Paths; import java.util.List; import java.util.stream.Collectors; import java.util.stream.Stream; public class FilesTest { public static void main(String[] args) throws Exception { // test1(); // test2(); // test3(); // test4(); // test5(); test6(); } public static void test1() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; // 可以指定编码 // Files.readAllLines(Paths.get(path), StandardCharsets.UTF_8); List<String> lines = Files.readAllLines(Paths.get(path)); for (String line : lines) { System.out.println(line); } } public static void test2() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; // 可以指定编码 // Files.newBufferedReader(Paths.get(path), StandardCharsets.UTF_8); try (BufferedReader bf = Files.newBufferedReader(Paths.get(path))) { String line; while ((line = bf.readLine()) != null) { System.out.println(line); } } } public static void test3() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; // 可以指定编码 // Files.lines(Paths.get(path), StandardCharsets.UTF_8); Stream<String> stringStream = Files.lines(Paths.get(path)); stringStream.forEach(line -> { System.out.println(line); }); } public static void test4() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; // 可以指定编码 // Files.lines(Paths.get(path), StandardCharsets.UTF_8); Stream<String> stringStream = Files.lines(Paths.get(path)); // 保证处理顺序 stringStream.forEachOrdered(line -> { System.out.println(line); }); } public static void test5() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; // 可以指定编码 // Files.lines(Paths.get(path), StandardCharsets.UTF_8); Stream<String> stringStream = Files.lines(Paths.get(path)); List<String> list = stringStream.collect(Collectors.toList()); for (String line : list) { System.out.println(line); } } / * 一次性读取整个文件 * @throws Exception */ public static void test6() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; // 可以指定编码 // Files.readAllLines(Paths.get(path), StandardCharsets.UTF_8); byte[] buffer = Files.readAllBytes(Paths.get(path)); // jdk11提供方法 // Files.readString(Paths.get(path)); System.out.println(new String(buffer)); } } 

5.1 小结

6 使用com.google.common.io.Files

package file.io.readfile; import com.google.common.io.Files; import java.io.BufferedReader; import java.io.File; import java.nio.charset.StandardCharsets; import java.util.List; / * @description: * @author: LiYuan * @date: 2024/7/24 11:34 */ public class FileTest2 { public static void main(String[] args) throws Exception { // test1(); test2(); } public static void test1() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; List<String> lines = Files.readLines(new File(path), StandardCharsets.UTF_8); for (String line : lines) { System.out.println(line); } } public static void test2() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; try (BufferedReader bf = Files.newReader(new File(path), StandardCharsets.UTF_8)) { String line; while ((line = bf.readLine()) != null) { System.out.println(line); } } } } 

6.1 小结

1）适合按行读取文件

7 使用org.apache.commons.io.FileUtils

package file.io.readfile; import org.apache.commons.io.FileUtils; import java.io.File; import java.nio.charset.StandardCharsets; import java.util.List; / * @description: * @author: LiYuan * @date: 2024/7/24 11:50 */ public class FileUtilsTest { public static void main(String[] args) throws Exception { // test1(); // test2(); test3(); } public static void test1() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; // 用编码字面值指定编码，例如 // List<String> lines = FileUtils.readLines(new File(path), “UTF-8"); // 或者使用默认编码 // List<String> lines = FileUtils.readLines(new File(path)) List<String> lines = FileUtils.readLines(new File(path), StandardCharsets.UTF_8); for (String line : lines) { System.out.println(line); } } public static void test2() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; // 用编码字面值指定编码，例如 // FileUtils.readFileToString(new File(path), “UTF-8"); // 或者使用默认编码 // FileUtils.readFileToString(new File(path)) String content = FileUtils.readFileToString(new File(path), StandardCharsets.UTF_8); System.out.println(content); } / * 读取整个文件到字节数组 * @throws Exception */ public static void test3() throws Exception { String path = "D:\\liyuan-gitee\\my-java-project\\myproj\\data\\file\\test1.txt"; byte[] buffer = FileUtils.readFileToByteArray(new File(path)); System.out.println(new String(buffer)); } } 

7.1 小结