9 Proven Ways to Read Files from the resources Folder in Spring Boot

This article presents nine methods to read files located in the resources directory of a Java project, especially when using Spring Boot.

/**
 * 根据文件路径读取文件内容
 *
 * @param fileInPath
 * @throws IOException
 */
public static void getFileContent(Object fileInPath) throws IOException {
    BufferedReader br = null;
    if (fileInPath == null) {
        return;
    }
    if (fileInPath instanceof String) {
        br = new BufferedReader(new FileReader(new File((String) fileInPath)));
    } else if (fileInPath instanceof InputStream) {
        br = new BufferedReader(new InputStreamReader((InputStream) fileInPath));
    }
    String line;
    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }
    br.close();
}

Method 1

The core approach uses getResource("") and getPath() to obtain the directory path.

public void function1(String fileName) throws IOException {
    String path = this.getClass().getClassLoader().getResource("").getPath(); // getResource("") is empty
    System.out.println(path);
    String filePath = path + fileName;
    System.out.println(filePath);
    getFileContent(filePath);
}

Method 2

This method directly calls getResource(fileName) to get the path and decodes it when the path contains Chinese characters.

/**
 * 直接通过文件名getPath来获取路径
 *
 * @param fileName
 * @throws IOException
 */
public void function2(String fileName) throws IOException {
    String path = this.getClass().getClassLoader().getResource(fileName).getPath();
    System.out.println(path);
    String filePath = URLDecoder.decode(path, "UTF-8"); // decode if Chinese characters are present
    System.out.println(filePath);
    getFileContent(filePath);
}

Method 3

Uses getFile() on the URL; getFile() includes query parameters while getPath() does not.

url.getFile() = /pub/files/foobar.txt?id=123456
url.getPath() = /pub/files/foobar.txt

Code example:

/**
 * 直接通过文件名+getFile()来获取
 *
 * @param fileName
 * @throws IOException
 */
public void function3(String fileName) throws IOException {
    String path = this.getClass().getClassLoader().getResource(fileName).getFile();
    System.out.println(path);
    String filePath = URLDecoder.decode(path, "UTF-8");
    System.out.println(filePath);
    getFileContent(filePath);
}

Method 4 (Important)

Uses getResourceAsStream to obtain an InputStream, which works inside a Spring Boot jar where no real file path exists.

/**
 * 直接使用getResourceAsStream方法获取流
 * springboot项目中需要使用此种方法，因为jar包中没有一个实际的路径存放文件
 *
 * @param fileName
 * @throws IOException
 */
public void function4(String fileName) throws IOException {
    InputStream in = this.getClass().getClassLoader().getResourceAsStream(fileName);
    getFileContent(in);
}

Method 5 (Important)

Also uses getResourceAsStream but without the class loader, accessing the file from the root of resources with a leading slash.

/**
 * 直接使用getResourceAsStream方法获取流
 * 如果不使用getClassLoader，可以使用getResourceAsStream("/配置测试.txt")直接从resources根路径下获取
 *
 * @param fileName
 * @throws IOException
 */
public void function5(String fileName) throws IOException {
    InputStream in = this.getClass().getResourceAsStream("/" + fileName);
    getFileContent(in);
}

Method 6 (Important)

Uses Spring's ClassPathResource to obtain an InputStream, recommended for Spring Boot projects.

/**
 * 通过ClassPathResource类获取，建议SpringBoot中使用
 * springboot项目中需要使用此种方法，因为jar包中没有一个实际的路径存放文件
 *
 * @param fileName
 * @throws IOException
 */
public void function6(String fileName) throws IOException {
    ClassPathResource classPathResource = new ClassPathResource(fileName);
    InputStream inputStream = classPathResource.getInputStream();
    getFileContent(inputStream);
}

Method 7

Retrieves the file using an absolute local path; not suitable for server environments.

/**
 * 通过绝对路径获取项目中文件的位置（不能用于服务器）
 * @param fileName
 * @throws IOException
 */
public void function7(String fileName) throws IOException {
    String rootPath = System.getProperty("user.dir"); // e.g., E:\WorkSpace\Git\spring-framework-learning-example
    String filePath = rootPath + "\\chapter-2-springmvc-quickstart\\src\\main\\resources\\" + fileName;
    getFileContent(filePath);
}

Method 8

Uses new File("") to get the current directory's absolute path; also only works locally.

/**
 * 通过绝对路径获取项目中文件的位置（不能用于服务器）
 * @param fileName
 * @throws IOException
 */
public void function8(String fileName) throws IOException {
    // 参数为空
    File directory = new File("");
    // 规范路径：getCanonicalPath() 方法返回绝对路径，会把 ..\ 、.\ 这样的符号解析掉
    String rootCanonicalPath = directory.getCanonicalPath();
    // 绝对路径：getAbsolutePath() 方法返回文件的绝对路径
    String rootAbsolutePath = directory.getAbsolutePath();
    System.out.println(rootCanonicalPath);
    System.out.println(rootAbsolutePath);
    String filePath = rootCanonicalPath + "\\chapter-2-springmvc-quickstart\\src\\main\\resources\\" + fileName;
    getFileContent(filePath);
}

Method 9

Sets an environment variable (e.g., TEST_ROOT) and builds the file path from it.

/**
 * 通过绝对路径获取项目中文件的位置
 *
 * @param fileName
 * @throws IOException
 */
public void function9(String fileName) throws IOException {
    System.setProperty("TEST_ROOT", "E:\\WorkSpace\\Git\\spring-framework-learning-example");
    // 参数为空
    String rootPath = System.getProperty("TEST_ROOT");
    System.out.println(rootPath);
    String filePath = rootPath + "\\chapter-2-springmvc-quickstart\\src\\main\\resources\\" + fileName;
    getFileContent(filePath);
}