简单实现的Servlet文件上传,并显示

原创
2013/08/28 15:15
阅读数 2.3W

大部分情况,会从HttpServletResponse取得PrintWriter实例,使用println()对浏览器进行字符输出。然而有时候,需要直接对浏览器进行字节输出,这时可以使用HttpServletResponse的getOutputStream()方法取得ServletOutputStream实例,它是OutputStream的子类。

image

如图,我们希望让浏览器直接输入PDF文件。

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 *  输出二进制字符
 * @author Barudisshu
 */
@WebServlet(name = "Download", urlPatterns = {"/download.do"})
public class Download extends HttpServlet {

    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String password = request.getParameter("password");
        if ("123456".equals(password)) {
            //设置MIME(Multipurpose Internet Mail Extensions)类型
            response.setContentType("application/pdf");
            //获取输入流对象
            InputStream in = getServletContext().getResourceAsStream("/WEB-INF/jdbc.pdf");
            //获取输出流对象
            OutputStream out = response.getOutputStream();
            //读取PDF并输出至浏览器
            writeBytes(in, out);
        }
    }

    private void writeBytes(InputStream in, OutputStream out)
            throws IOException {
        byte[] buffer = new byte[1024];
        int length = -1;
        while ((length = in.read(buffer)) != -1) {
            out.write(buffer, 0, length);
        }
        in.close();
        out.close();
    }
}

上传文件,并显示在客户端。

代码清单1:upload.xhtml (上传表单)

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>上传文件</title>
        <style type="text/css">
            .container{
                margin: 0 auto;
                width: 400px;
                border:thin solid #84d44f;
                padding: 100px;
            }
        </style>
    </head>
    <body>
        <div class="container">
            <form action="upload.do" method="post" enctype="multipart/form-data">
                <table>
                    <tr>
                        <td><label for="file">上传文件:</label></td>
                        <td><input type="file" id="file" name="picture" value=""/></td>
                    </tr>
                    <tr>
                        <td colspan="2"><input type="submit" value="提交"/></td>
                    </tr>
                </table>
            </form>
        </div>
    </body>
</html>

代码清单2:UploadServlet.java (获取请求,并输入到服务器目录)

/**
 * Function 负责文件的上传,并返回结果
 * @author Barudisshu
 */
@MultipartConfig
@WebServlet(name = "UploadServlet", urlPatterns = {"/upload.do"})
public class UploadServlet extends HttpServlet {

    private String contextPath;

    @Override
    public void init() throws ServletException {
        contextPath = getServletContext().getRealPath("/");
    }

    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        Part part = request.getPart("picture");
        String fileName = getFileName(part);
        writeTo(fileName, part);

        //forward到显示
        request.setAttribute("fileName", fileName);
        request.getRequestDispatcher("show.jsp").forward(request, response);
    }

    //取得上传文件名
    private String getFileName(Part part) {
        String header = part.getHeader("Content-Disposition");
        String fileName = header.substring(header.indexOf("filename=\"") + 10,
                header.lastIndexOf("\""));
        return fileName;
    }

    //存储文件
    private void writeTo(String fileName, Part part) throws IOException, FileNotFoundException {
        InputStream in = part.getInputStream();
        OutputStream out = new FileOutputStream(contextPath + fileName);
        byte[] buffer = new byte[1024];
        int length = -1;
        while ((length = in.read(buffer)) != -1) {
            out.write(buffer, 0, length);
        }
        in.close();
        out.close();
    }
}

这里有很多限制,这使用的是Servlet 3.0 新的特征标注(Annotaion)类描述部署,一些低版本的服务器需要使用标准依赖部署描述文件(web.xml)来部署,另外Part也是Java EE 6.0新增的类,Part是一个接口继承于javax.servlet.http,代表一部分表单项目接收来自multipart/form-data的POST的请求。

 

代码清单3:show.jsp (显示类)

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
        <h1>图片显示</h1>
        <a href="${fileName}">${fileName}</a>
    </body>
</html>

这里使用EL表达式描述,优化了代码。

下面给出效果链接……

http://phantom.duapp.com/upload.xhtml

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