java 通过 InputStream 判断文件编码格式

方法一

/**
	 * 判断文件的编码格式
	 *
	 * @return 文件编码格式
	 */
	public static String getFileCode(InputStream in) {
		try {
			int p = (in.read() << 8) + in.read();
			String code = "GBK";

			switch (p) {
				case 59524:
					code = "UTF-8";
					break;
				case 0xfffe:
					code = "Unicode";
					break;
				case 0xfeff:
					code = "UTF-16BE";
					break;
				case 48581:
					code = "GBK";
					break;
				default:
			}
			return code;
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

通过引用大佬的文章并且修改 UTF-8 的值得到上面的代码，仅支持少部分编码格式，

https://my.oschina.net/lipengxs

方法二

使用juniversalchardet提供的方法，很全面。推荐使用

POM

 <dependency>
    <groupId>com.github.albfernandez</groupId>
    <artifactId>juniversalchardet</artifactId>
    <version>2.4.0</version>
 </dependency>

code

 private static String getFileCharacter(String fileName) {
        byte[] buf = new byte[4096];
        try (InputStream inputStream = Files.newInputStream(Paths.get(fileName))) {
            UniversalDetector detector = new UniversalDetector();

            int nread;
            while ((nread = inputStream.read(buf)) > 0 && !detector.isDone()) {
                detector.handleData(buf, 0, nread);
            }
            detector.dataEnd();

            String encoding = detector.getDetectedCharset();
            detector.reset();
            if (Objects.isNull(encoding)) {
                throw new IllegalArgumentException("No encoding detected.");
            }
            return encoding;
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

test

 public static void main(String[] args) {
        String fileName = "C:\\Users\\SERVER\\Downloads\\A.csv";
        String fileCharacter = getFileCharacter(fileName);
        System.out.println("fileCharacter = " + fileCharacter);
    }
    
## output
fileCharacter = GB18030

关于GB18030、GB2312、GBK的区别 请参考

https://zhuanlan.zhihu.com/p/453675608