避免在Java中使用多个If语句

Question

我已经编写了类似这样的方法。但是我猜这应该进行重构。谁能建议最好的方法来避免使用多个if语句？

private String getMimeType(String fileName){
  if(fileName == null) {
    return "";   
  } 
  if(fileName.endsWith(".pdf")) {
    return "application/pdf";   
  }
  if(fileName.endsWith(".doc")) {
    return "application/msword";  
  }
  if(fileName.endsWith(".xls")) {
    return "application/vnd.ms-excel"; 
  }
  if(fileName.endsWith(".xlw")) {
    return "application/vnd.ms-excel"; 
  }
  if(fileName.endsWith(".ppt")) {
    return "application/vnd.ms-powerpoint"; 
  }
  if(fileName.endsWith(".mdb")) {
    return "application/x-msaccess"; 
  }
  if(fileName.endsWith(".rtf")) {
    return "application/rtf"; 
  }
  if(fileName.endsWith(".txt")) {
    return "txt/plain"; 
  }
  if(fileName.endsWith(".htm") || fileName.endsWith(".html")) {
    return "txt/html"; 
  }
  return "txt/plain"; 
}

我在这里不能使用大小写转换，因为我的“条件”是java.lang.String。

Answer 1

您可以使用Map来保存您的解决方案：

Map<String,String> extensionToMimeType = new HashMap<String,String>();
extensionToMimeType.put("pdf", "application/pdf");
extensionToMimeType.put("doc", "application/msword");
// and the rest

int lastDot = fileName.lastIndexOf(".");
String mimeType;
if (lastDot == -1) {
    mimeType = NO_EXTENSION_MIME_TYPE;
} else {
    String extension = fileName.substring(lastDot+1);
    mimeType = extensionToMimeType.getOrDefault(extension, 
                                                UNKNOWN_EXTENSION_MIME_TYPE);
}

为了使此代码起作用，您需要像在类中那样进行定义NO_EXTENSION_MIME_TYPE和定义UNKNOWN_EXTENSION_MIME_TYPE，如下所示：

private static final String NO_EXTENSION_MIME_TYPE = "application/octet-stream";
private static final String UNKNOWN_EXTENSION_MIME_TYPE = "text/plain";