| 数据库, javaweb, 图片的上传下载

图片的上传和下载以及存入数据库

首先添加jar包

这里我直接写maven依赖

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.1.0</version>
</dependency>
<dependency>
    <groupId>commons-fileupload</groupId>
    <artifactId>commons-fileupload</artifactId>
    <version>1.3.3</version>
</dependency>
<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.5</version>
</dependency>
<dependency>
    <groupId>commons-logging</groupId>
    <artifactId>commons-logging</artifactId>
    <version>1.2</version>
    <type>pom.lastUpdated</type>
</dependency>

表单：

<form action="Aservlet" method="post" enctype="multipart/form-data">
    <input type="text" name="tname" />
    <input type="file" name="tfile" />
    <button type="submit">SSSS</button>
</form>

这里注意enctype的值

创建一个Servlet处理接收数据

PrintWriter out=response.getWriter();
response.setContentType("text/html");

try {
    DiskFileItemFactory factory=new DiskFileItemFactory();
    ServletFileUpload upload=new ServletFileUpload(factory);
    upload.setHeaderEncoding("utf-8");
    if(!ServletFileUpload.isMultipartContent(request)) {
        return;
    }
    List<FileItem> list=upload.parseRequest(request);
    for (FileItem fileItem : list) {
        if(fileItem.isFormField()) {
            //处理表单内非文件内容
            String name=fileItem.getFieldName();
            String value=fileItem.getString("UTF-8");

        }else {
            String filename=fileItem.getName();
            if(filename.endsWith(".png")) {
                //这里只接收以png结尾的文件
                filename=filename.substring(filename.lastIndexOf("\\")+1);
                //得到文件输入流
                InputStream inputStream=fileItem.getInputStream();        
                //创建一个新数组存放内容
                byte data[]=new byte[inputStream.available()];
                //写入数组
                inputStream.read(data);
                /*byte buffer[]=new byte[1024];
                int len=0;
                while((len=inputStream.read(buffer))>0) {
                    outputStream.write(buffer, 0, len);
                }*/
                inputStream.close();
                //用base64编码为字符串，接下来就能存入数据库（未写）
                String str=Base64.getEncoder().encodeToString(data);
                request.getSession().setAttribute("img", str);

                fileItem.delete();
            }
            else {
                continue;
            }
        }
    }


}catch (Exception e) {
    // TODO: handle exception
}
request.getRequestDispatcher("img.jsp").forward(request, response);

这里是doget()里的内容

创建输出图片的servlet

//禁止缓存
response.setDateHeader("Expires", -1);
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
// 通知jsp以图片方式打开发送过去的数据
response.setHeader("Content-Type", "image/jpeg");
String str=(String) request.getSession().getAttribute("img");
OutputStream outputStream=response.getOutputStream();
byte data[]=Base64.getDecoder().decode(str);
outputStream.write(data);
outputStream.close();

base64解码，用response的输出流输出

显示图片的jsp

<label>图片:</label>
<img width="200" height="200" src="${pageContext.request.contextPath}/Imgg"/>
<a href="${pageContext.request.contextPath}/DownS">hahah</a>

可以设置图片的高和宽

下载图片

通过上面的超链接请求downs这个servlet下载图片
doget()内容

response.setDateHeader("Expires", -1);
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
response.setHeader("content-disposition", "attachment;");
String str=(String) request.getSession().getAttribute("img");
OutputStream outputStream=response.getOutputStream();
byte data[]=Base64.getDecoder().decode(str);
outputStream.write(data);
outputStream.close();

遇到的错误或异常：
使用EL表达式标红
缺少commons-logging

ESC