用java的servlet实现http访问mongodb中的文件

一个java的servlet文件（FileCtrl .java）： 

import com.mongodb.BasicDBObject;  import com.mongodb.DBObject;  import com.mongodb.gridfs.GridFSDBFile;  import java.io.IOException;  import java.net.URLDecoder;  import java.text.DateFormat;  import java.text.ParseException;  import java.text.SimpleDateFormat;  import java.util.Date;  import java.util.Locale;  import java.util.TimeZone;  import javax.servlet.ServletException;  import javax.servlet.http.HttpServlet;  import javax.servlet.http.HttpServletRequest;  import javax.servlet.http.HttpServletResponse;      public class FileCtrl extends HttpServlet {     private static final long serialVersionUID = -1504839175114429753L;        private Date getDateByString(String format, String dateStr) throws ParseException{    SimpleDateFormat sdf = new SimpleDateFormat(format);       return sdf.parse(dateStr);   }        private boolean needCache(String ext){//判断文件是否需要缓存。          if(ext == null){              return false;          }          boolean need = false;          String[] arr = {"jpg", "jpeg", "png", "gif", "bmp", "html", "htm", "swf", "mp3", "mp4", "pdf"};          for(String s : arr){              if(s.equals(ext)){                  need = true;                  break;              }          }          return need;      }           private String getContentType(String ext){          String type = null;          if(ext == null){              type = "application/octet-stream";          }          else if(ext.equals("jpg")){              type = "image/jpeg";          }          else if(ext.equals("jpeg") || ext.equals("png") || ext.equals("gif") || ext.equals("bmp")){              type = "image/" + ext;          }          else if(ext.equals("html") || ext.equals("htm")){              type = "text/html; charset=utf-8";          }          else if(ext.equals("swf")){              type = "application/x-shockwave-flash";          }          else if(ext.equals("mp3")){              type = "audio/x-mpeg";          }          else if(ext.equals("mp4")){              type = "video/mp4";          }          else if(ext.equals("pdf")){              type = "application/pdf";          }          else{              type = "application/octet-stream";          }          return type;      }           @Override      protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {       response.setContentType("text/html; charset=utf-8");          String url = URLDecoder.decode(request.getRequestURI(), "utf-8");  //doget方法可以访问带汉字的url          int second = url.indexOf("/files/", 1);          url = url.substring(second + 7);          String[] arr = url.split("/");          DBObject query = new BasicDBObject("filename", arr[2]);          query.put("type", arr[0]);          try {     query.put("publishDate", getDateByString("yyyy-MM-dd", arr[1]));    } catch (ParseException e1) {     System.out.println(e1.getMessage());    }   GridFS fs = new GridFS(mongo.getDB(database));//连接mongodb数据库；细节就不详述。          GridFSDBFile f = fs.getFs().findOne(query);          if(f == null){           PubFun.ajaxPrintC("此文件不存在！", response);          }else{              String ext = null;              int index = arr[2].lastIndexOf(".");              if(index > 0){                  ext = arr[2].substring(index+1).toLowerCase();              }              response.setContentType(getContentType(ext));              if(needCache(ext)){                  String modifiedSince = request.getHeader("If-Modified-Since");                  DateFormat df = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.ENGLISH);                  df.setTimeZone(TimeZone.getTimeZone("GMT"));                  Date uploadDate = f.getUploadDate();                  String lastModified = df.format(uploadDate);                  if(modifiedSince != null){                      Date modifiedDate = null;                      Date sinceDate = null;                      try{                          modifiedDate = df.parse(lastModified);                          sinceDate = df.parse(modifiedSince);                      }catch(ParseException e){                       System.out.println(e.getMessage());                      }                      if(modifiedDate.compareTo(sinceDate) <= 0){                          response.setStatus(304);    //Not Modified                          return;                      }                  }                  long maxAge = 10L * 365L * 24L * 60L * 60L;    //ten years, in seconds                  response.setHeader("Cache-Control", "max-age=" + maxAge);                  response.setHeader("Last-Modified", lastModified);                  response.setDateHeader("Expires", uploadDate.getTime() + maxAge * 1000L);              }else{                  response.setHeader("Pragma","no-cache");                  response.setHeader("Cache-Control","no-cache");                  response.setDateHeader("Expires", 0);              }              f.writeTo(response.getOutputStream());          }      }        @Override      protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        }       }

可以通过FileCtrl来获取，在web.xml中配置如下：

 <servlet>       <servlet-name>files</servlet-name>       <servlet-class>FileCtrl</servlet-class>   </servlet>   <servlet-mapping>       <servlet-name>files</servlet-name>       <url-pattern>/files/*</url-pattern>   </servlet-mapping>