springboot 下载mongodb文档，并支持在线预览

1、工具类

import org.springframework.core.io.ByteArrayResource;
import org.springframework.core.io.Resource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.Base64;

public class FileDownLoadUtils {

   /**
    * 下载文件或者在线预览文件，在线预览只支持jpg,png等
    *
    * @param filename  下载的文件名称
    * @param bytes     文件转换的字节码
    * @param review    是否在线预览
    * @param userAgent 浏览器类型  使用 request.getHeader("User-Agent")获取
    * @return
    * @throws UnsupportedEncodingException
    */
   public static ResponseEntity<Resource> download(String filename, byte[] bytes, boolean review,
                                                   String userAgent) throws UnsupportedEncodingException
   {
      return download(filename, bytes, review ? parseMediaType(filename) : MediaType.APPLICATION_OCTET_STREAM,
         userAgent);
   }

   private static ResponseEntity<Resource> download(String filename, byte[] bytes, MediaType mediaType,
                                                   String userAgent) throws UnsupportedEncodingException
   {
      HttpHeaders headers = new HttpHeaders();
      headers.add("Cache-Control", "no-cache, no-store, must-revalidate");
      headers.add("Pragma", "no-cache");
      headers.add("Expires", "0");
      headers.add("charset", "utf-8");
      String finalName = URLEncoder.encode(filename, "UTF-8");
      if(userAgent != null) {
         if(userAgent.toLowerCase().indexOf("firefox") > -1) {
            finalName = "=?UTF-8?B?" + new String(Base64.getEncoder().encode(filename.getBytes("UTF-8"))) + "?=";
         }
         else if(userAgent.toLowerCase().indexOf("safari") > -1) {
            finalName = new String(finalName.getBytes("UTF-8"), "ISO8859-1");
         }
      }

      headers.add("Content-Disposition", "filename=\"" + finalName + "\"");
      return ((ResponseEntity.BodyBuilder) ResponseEntity.ok().headers(headers)).contentLength((long) bytes.length)
                                                                                .contentType(mediaType)
                                                                                .body(new ByteArrayResource(bytes));
   }

   /**
    * 根据文件名称转换文件
    * @param fileName
    * @return
    */
   public static MediaType parseMediaType(String fileName) {
      MediaType mediaType = MediaType.APPLICATION_OCTET_STREAM;
      int dot = fileName != null ? fileName.lastIndexOf(".") : -1;
      if(dot < 0) {
         return mediaType;
      }
      else {
         String suffix = fileName.substring(dot + 1).toUpperCase();
         if(suffix.equalsIgnoreCase("GIF")) {
            mediaType = MediaType.IMAGE_GIF;
         }
         else if(suffix.equalsIgnoreCase("PNG")) {
            mediaType = MediaType.IMAGE_PNG;
         }
         else if(!suffix.equalsIgnoreCase("JPG") && !suffix.equalsIgnoreCase("JPEG")) {
            if(suffix.equalsIgnoreCase("XML")) {
               mediaType = MediaType.APPLICATION_XML;
            }
            else if(suffix.equalsIgnoreCase("PDF")) {
               mediaType = MediaType.APPLICATION_PDF;
            }
         }
         else {
            mediaType = MediaType.IMAGE_JPEG;
         }

         return mediaType;
      }
   }
}

2、service

import cn.test.authention.service.FileManagerService;
import cn.test.maple.document.util.FileUtil;
import com.mongodb.client.gridfs.GridFSBucket;
import com.mongodb.client.gridfs.model.GridFSFile;
import org.bson.types.ObjectId;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.Resource;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.data.mongodb.gridfs.GridFsTemplate;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;

import java.io.ByteArrayOutputStream;

@Service
public class FileManagerServiceImpl implements FileManagerService {
   private static final Logger log = LoggerFactory.getLogger(FileManagerServiceImpl.class);

   @Autowired
   private GridFsTemplate gridFsTemplate;

   @Autowired
   private GridFSBucket gridFSBucket;

   private byte[] getFileBytes(String id) {
      ByteArrayOutputStream out = new ByteArrayOutputStream(2048);
      gridFSBucket.downloadToStream(new ObjectId(id), out);
      return out.toByteArray();
   }

   public ResponseEntity<Resource> downloadFile(String id, boolean review, String userAgent) throws Exception{
      Query query = Query.query(Criteria.where("_id").is(id));
      // 查询单个文件
      GridFSFile gridFSFile = gridFsTemplate.findOne(query);

      if(gridFSFile == null) {
         log.warn("下载的文件不存在");
         throw new RuntimeException("文件不存在");
      }

      String fileName = gridFSFile.getFilename().replace(",", "");
      byte[] bytes = getFileBytes(id);
      return FileUtil.download(fileName, bytes, review, userAgent);
   }
}

配置类

import com.mongodb.client.MongoDatabase;
import com.mongodb.client.gridfs.GridFSBucket;
import com.mongodb.client.gridfs.GridFSBuckets;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.mongodb.MongoDbFactory;

@Configuration
public class MongodbConfig {
   @Autowired
   private MongoDbFactory mongoDbFactory;

   @Bean
   public GridFSBucket getGridFSBucket() {

      MongoDatabase db = mongoDbFactory.getDb();
      return GridFSBuckets.create(db);
   }

}

需要引的包

compile 'org.springframework.boot:spring-boot-starter-data-mongodb'