java 传递一个 文件后缀 例如 csv获取对应的 mimeType

可以使用 Java 内置的 MIME 类型映射表来获取文件后缀对应的 MIME 类型。具体实现代码如下：

import java.util.HashMap;
import java.util.Map;

public class MimeTypeUtils {
    
    private static final Map<String, String> MIME_TYPES = new HashMap<String, String>() {{
        put("csv", "text/csv");
        put("doc", "application/msword");
        put("docx", "application/vnd.openxmlformats-officedocument.wordprocessingml.document");
        put("gif", "image/gif");
        put("jpeg", "image/jpeg");
        put("jpg", "image/jpeg");
        put("pdf", "application/pdf");
        put("png", "image/png");
        put("ppt", "application/vnd.ms-powerpoint");
        put("pptx", "application/vnd.openxmlformats-officedocument.presentationml.presentation");
        put("txt", "text/plain");
        put("xls", "application/vnd.ms-excel");
        put("xlsx", "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
        put("zip", "application/zip");
    }};

    /**
     * 根据文件后缀获取对应的 MIME 类型
     *
     * @param fileExtension 文件后缀，如 .csv
     * @return MIME 类型，如 text/csv
     */
    public static String getMimeType(String fileExtension) {
        return MIME_TYPES.getOrDefault(fileExtension.toLowerCase(), "application/octet-stream");
    }
}

使用方法如下：

String mimeType = MimeTypeUtils.getMimeType(".csv");
System.out.println(mimeType); // 输出 text/csv
``