java 读取各种类型的文件 （三）

后端java，springboot 、前端vue： 对 txt文件的读写，以及前端预览

一、后端读

　　public void readTxt() {

                InputStreamReader input = null;
                BufferedReader buffer_reader = null;
　　　　　　　　　 ArrayBlockingQueue<String[]> fileData = new ArrayBlockingQueue<String[]>(50000);

                try {
                    input = new InputStreamReader(new FileInputStream(new File(xxx)), Charset.forName("UTF-8"));
                    buffer_reader = new BufferedReader(input, 2048); // 2MB 缓存空间
                    String line_str = null;
                    while ((line_str = buffer_reader.readLine()) != null) {
                            String[] lines = line_str.split(regexStr);
                            fileData.put(lines);
                    }
                } catch (Exception e) {
                    try {
                        buffer_reader.close();
                    } catch (Exception e1) {
                    }
                    try {
                        input.close();
                    } catch (Exception e1) {
                    }
                    LOGGER.error("读取TXT文件失败{}",e);
                }
            }
        }
二、后端写

public void run() {
            File file = new File("X:/new.txt");
            if(!file.exists()){
                try {
                    file.createNewFile();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        try {
            BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file)));
            try {
                bufferedWriter.write("hello,world!\nI like the world!");
            } catch (IOException e) {
                e.printStackTrace();
            }finally {
                try {
                    bufferedWriter.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}

三、前后端配合预览
　　1、controller类中
　 public ResponseEntity<byte[]> previewFile(@RequestBody FileVO fileVO) {

        if(fileVO == null || fileVO.getId() == null){
            return null;
        }
        String filename = fileVO.getFileName();
        byte[] buffer = getTxTBytes(fileVO,30);
 　　　　HttpHeaders headers = new HttpHeaders();

        //防止中文名乱码
        //filename = new String(filename.getBytes(StandardCharsets.UTF_8), StandardCharsets.ISO_8859_1);
        try {
            headers.setContentDispositionFormData("attachment",  filename=java.net.URLEncoder.encode(filename, "UTF-8"));
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        headers.add(HttpHeaders.CONTENT_TYPE,"application/octet-stream;charset=UTF-8");
        headers.add("file-type",smsTaskFile.getFileType());
        //返回
        return new ResponseEntity<byte[]>(buffer, headers, HttpStatus.CREATED);
    }

   private byte[] getTxTBytes(FileVO fileVO, int preLines) {
    　　byte[] fileBuffer = null;
    　　int readLine = 0;
    　　InputStreamReader reader = null;
    　　BufferedReader buffer_reader = null;
    　　try {
    　　    reader = new InputStreamReader(new FileInputStream(fileVO.getFilePath()), Charset.forName("UTF-8"));
　　　　　　 buffer_reader = new BufferedReader(reader, 20480); // 2MB 缓存空间
 　　　　　　String line_str = null;

   　　     StringBuilder content = new StringBuilder("");
   　　     while ((line_str = buffer_reader.readLine()) != null && readLine < preLines) {
  　　          content.append(line_str).append("\n");
  　　          readLine++;
 　　       }
 　　       fileBuffer = content.toString().getBytes(StandardCharsets.UTF_8);
　　    } catch (Exception e) {
    　　    try {
   　　         buffer_reader.close();
  　　      } catch (Exception e1) {
  　　      }
   　　     try {
    　　        reader.close();
    　　    } catch (Exception e1) {
    　　    }
    　　    LOGGER.error("读取TXT文件失败{}",e);
   　　 }
  　　  return fileBuffer;
　　}

　　2、vue

<el-button v-if="item.key == 'operate'" @click.stop="taskfilePreview(scope.row)" type="text" size="small">预览</el-button>

<el-dialog-side :visible="showPreviewFile" @close="showPreviewFile = false;fileContent=''">

  <h1>只预览文件前30行</h1><br>
  <el-card>
    <el-input v-if="fileContent"
              v-model="fileContent"
              show-word-limit
              :autosize="{ minRows: 12}"
              type="textarea"
    ></el-input>
  </el-card>
</el-dialog-side>

taskfilePreview(row){
  const reader = new FileReader();

  //通过readAsArrayBuffer将blob转换为ArrayBuffer对
  Actions.previewFile(row).then(res => {
    if (res.data) {
      reader.readAsText(res.data) // 这里的res.data是blob文件流
      reader.onload = (event) => {
        var data = event.target.result;
        this.showPreviewFile = true
        this.fileContent = data
      }
    }
  })
}