下面进一步优化：
具体逻辑 ：删除原数据表Test，路径等文件信息依旧存log_file表。文件预览时，判断文件类型，如果为word类型，进行转换pdf展示；反之直接展示文件。
word类型条件满足后，进一步判断文件是否已经转换过(判断依据是根据路径下文件名查找相同文件名的pdf文件是否存在)，如果同名的pdf文件存在，表示已经转换过，直接展示；如果不存在，word转换pdf，再展示。

代码如下：

public void world(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws IOException {
        List<LogFile> files = terminalServiceImpl.world();
        //用作实例展示，在这取得是数据库第二条信息：以word文件展示。
        String path = files.get(1).getFilePath();
        String filename=files.get(1).getFileName();
        //1.根据文件后缀获取文件类型
        File wordName=new File(filename);
        String fileName=wordName.getName();
        String fileTyle=fileName.substring(fileName.lastIndexOf("."),fileName.length());
        logger.info("------文件后缀名------"+fileTyle);
        //如果文件类型为word,需要先转换成pdf
        if(fileTyle.equals(".doc")||fileTyle.equals(".docx")){
                //1.判断文件是否已经转换pdf,文件是否存在：文件前缀+.pdf(word是否已经转换过pdf)，如果存在直接展示pdf
                File fileOne = new File(path);
                String caselsh = filename.substring(0,filename.lastIndexOf("."));
                logger.info("------pdf文件名字------"+caselsh+"pdf.pdf");
//                File fileIf = new File(fileOne+"\\" + caselsh+".pdf");
                String filePath=(fileOne+"\\" + caselsh+"pdf.pdf");
                File fileIf=new File(filePath);
                if(!fileIf.exists()){
                    String pdfFilePath = OpenOfficeUtil.wordToPDF(path,filename);
                    System.err.println(pdfFilePath);
                    FileInputStream fileInputStream = new FileInputStream(pdfFilePath);
                    byte[] content = new byte[fileInputStream.available()];
                    fileInputStream.read(content);
                    fileInputStream.close();
                    ServletOutputStream servletOutputStream = httpServletResponse.getOutputStream();
                    if (servletOutputStream != null && content != null){
                        httpServletResponse.setContentType("application/pdf");
                        httpServletResponse.setContentLength(content.length);
                        httpServletResponse.setHeader("Expires","0");
                        httpServletResponse.setHeader("Cache-Control","must-revalidate,post-check=0,pre-check=0");
                        httpServletResponse.setHeader("Pragma","public");
                        servletOutputStream.write(content);
                        servletOutputStream.flush();
                        servletOutputStream.close();
                }else{
                    File file3 = new File(filePath);
                    //获取pdf文件路径,内容做展示
                    byte[] resultE = new byte[(int) file3.length()];
                    FileInputStream fis = new FileInputStream(file3);
                    fis.read(resultE); //read file into bytes[]
                    fis.close();
                    ServletOutputStream servletOutputStream = httpServletResponse.getOutputStream();
                    if (servletOutputStream != null && resultE != null){
                        httpServletResponse.setContentType("application/pdf");
                        httpServletResponse.setContentLength(resultE.length);
                        httpServletResponse.setHeader("Expires","0");
                        httpServletResponse.setHeader("Cache-Control","must-revalidate,post-check=0,pre-check=0");
                        httpServletResponse.setHeader("Pragma","public");
                        servletOutputStream.write(resultE);
                        servletOutputStream.flush();
                        servletOutputStream.close();
        }else{
            File file = new File(path);
            File file2 = new File(file+"\\" + filename);
            //获取pdf文件路径,内容做展示
            byte[] result = new byte[(int) file2.length()];
            FileInputStream fis = new FileInputStream(file2);
            fis.read(result); //read file into bytes[]
            fis.close();
            ServletOutputStream servletOutputStream = httpServletResponse.getOutputStream();
            if (servletOutputStream != null && result != null){
                httpServletResponse.setContentType("application/pdf");
                httpServletResponse.setContentLength(result.length);
                httpServletResponse.setHeader("Expires","0");
                httpServletResponse.setHeader("Cache-Control","must-revalidate,post-check=0,pre-check=0");
                httpServletResponse.setHeader("Pragma","public");
                servletOutputStream.write(result);
                servletOutputStream.flush();
                servletOutputStream.close();