java - java中super不能作为构造函数第一行时的解决方法

Question

我正在使用将本地文件作为输入的 CSVReader 类。但是现在，我需要能够读取本地文件以及具有 URL 路径的文件(如 http://example.com/example.txt )。为此，我想从 CSVReader 派生一个类来标识文件是本地文件还是 URL，然后在构造函数的第一行中使用 super() 将 InputStream 传递给父级。这样做的优雅方式是什么？

public class FileReader extends CsvReader{
    public FileReader(){
        if (fileName != null) {

               if (fileName.trim().startsWith("http:")) {
                // it is URL
                URL url = new URL(fileName);
                inputStream = new BufferedReader(new InputStreamReader(
                        url.openStream(), charset),
                        StaticSettings.MAX_FILE_BUFFER_SIZE); 
               }else{
                //it is a local file
                inputStream = new BufferedReader(new InputStreamReader(
                        new FileInputStream(fileName), charset),
                        StaticSettings.MAX_FILE_BUFFER_SIZE);
               } 

            }
            //Now pass the input stream to CsvReader
            super(inputStream, delimiter, charset);  //error - super has to be first line of constructor
    }
}

Answer 1

可以编写辅助方法:

super(createReader(createInputStream(resouce), "UTF-8"), ";");

您的辅助方法可能如下所示:

public static InputStream createInputStream(String resource)
{
     resource = resource.trim();

     if (resource.startsWith("http:"))
     {
          return new URL(resource).openStream();
     } else
     {
          return new FileInputStream(new File(resource));
     }
}

public static BufferedReader createReader(InputStream is, String charset)
{
     return new BufferedReader(new InputStreamReader(is, charset));
}