避免在Java中使用多个If语句 [英] Avoiding multiple If statements in Java

问题描述

我已经编写了类似这样的方法.但是我想应该对它进行重构.有人可以建议最好的方法来避免使用多个if语句吗?

I've coded a method something like this. But I guess this should undergo refactoring. Can any one suggest the best approach to avoid using this multiple if statements?

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 .

I cannot use switch-case here as my 'condition' is a java.lang.String.

推荐答案

您可以使用

You can use a Map to hold your solutions:

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);
}

要使此代码正常工作，您需要像在类中那样定义 NO_EXTENSION_MIME_TYPE 和 UNKNOWN_EXTENSION_MIME_TYPE ，如下所示:

For this code to work you'll need to have defined NO_EXTENSION_MIME_TYPE and UNKNOWN_EXTENSION_MIME_TYPE as in your class, somewhat like this:

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

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