关于文件上传的坑，tomcat一重启图片就消失

首先在tomcat的conf的server.xml中配置一个配置.

记得要找到Host标签。在这个标签里面添加

 <Context path ="/File" docBase ="D:/File" debug ="0" privileged ="true">
        </Context>

最终效果是这样的:

 <Host name="localhost"  appBase="webapps"
            unpackWARs="true" autoDeploy="true">

        <!-- SingleSignOn valve, share authentication between web applications
             Documentation at: /docs/config/valve.html -->
        <!--
        <Valve className="org.apache.catalina.authenticator.SingleSignOn" />
        -->
        <Context path ="/File" docBase ="D:/File" debug ="0" privileged ="true">
        </Context>
        <!-- Access log processes all example.
             Documentation at: /docs/config/valve.html
             Note: The pattern used is equivalent to using pattern="common" -->
        <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
               prefix="localhost_access_log" suffix=".txt"
               pattern="%h %l %u %t &quot;%r&quot; %s %b" />

      </Host>

在后台用的时候就可以这样写

String productName = req.getParameter("productName");
        String productDesc = req.getParameter("productDesc");
        String productPrice = req.getParameter("productPrice");
        Part cover = req.getPart("productImage");
        Long da = new Date().getTime()/1000;
        String filePath = "/"+da+"_"+cover.getSubmittedFileName();
        File file = new File("/File"); //这里是重点
        String destPath = file.getAbsolutePath()+filePath;
        new File(destPath).getParentFile().mkdir();
        cover.write(destPath);
        int categoryId = Integer.parseInt(req.getParameter("categoryId"));
        Product product = new Product(productName,productDesc,new BigDecimal(productPrice),filePath,categoryId);
        ProductService service = new ProductService();
        service.insertProduct(product);
        resp.sendRedirect(req.getContextPath()+"/index");

上面我标记的地方就会去找D://File

idea里面在配置一个东西

在上面的HTTP port 右侧点上勾

就可以用在jsp使用了

  <img id="image" src="/File${product.productImage}" style=" 100px" >