避免Java中的多个If语句

我已经编写了一个这样的方法.但我想这应该重构.

任何人可以建议避免使用这个多个if语句的最佳方法？

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"; 
}

我不能在这里使用switch-case,因为我的’condition’是一个java.lang.String.

解决方法

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.get(extension);
    if (mimeType == null) {
        mimeType = UNKNOWN_EXTENSION_MIME_TYPE;
    }
}

为使该代码工作,你需要定义NO_EXTENSION_MIME_TYPE和UNKNOWN_EXTENSION_MIME_TYPE在你的课,有点像这样：

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