JavaEE拾遗01--异步上传文件

今天学习了JavaEE的Servlet的异步调用和文件上传，合着做了一个异步上传文件练习，注意到Servlet是多线程的，所以实际操作中不需要异步操作（我是这么觉得的），闲话少说，看代码

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>文件上传</title>
</head>
<body>
<form method="post" action="../upload" enctype="multipart/form-data">
  文件名：<input type="text" id="name" name="name" /><br />
选择上传文件：<input type="file" id="file" name="file" />
<input type="submit" value="上传" />
</form>
</body>
</html>

上面写了一个jsp页面，这个页面的<input type="file" /> 和<form method="post" action="../upload" enctype="multipart/form-data">是可以实现文件上传的秘密

接下来是处理文件上传的servlet

package liujie.jee.uploadfile;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.AsyncContext;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import liujie.jee.bean.UploadFileExecutor;

//使用注解表示这个servlet支持异步操作，
@WebServlet(urlPatterns = { "/upload" }, name = "upload", asyncSupported = true)
// 处理文件上传的servlet需要使用MultipartConfig标识
@MultipartConfig
public class UploadFileServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        // 得到文件名
        String fileName = request.getParameter("name");
        out.println("开始上传文件：" + fileName + ".</br>");
        // 示例化异步调用
        AsyncContext asct = request.startAsync();
        // 设置任务超时时间为10分钟
        asct.setTimeout(10 * 60 * 1000);
        // 设置异步调用的监听器，当调用完成时提示
        asct.addListener(new AsyncListener() {

            // 出错时调用
            @Override
            public void onError(AsyncEvent event) {
            }

            // 完成时调用
            @Override
            public void onComplete(AsyncEvent event) {
                out.println("文件：" + fileName + "上传完毕");
            }

            // 开始时调用
            @Override
            public void onStartAsync(AsyncEvent event) {
            }

            // 超时时调用
            @Override
            public void onTimeout(AsyncEvent event) {
            }
        });
        asct.start(new UploadFileExecutor(asct));
        /*
         * out.println("文件大小为：" + fileSize + "</br>"); out.println("上传文件的类型是：" +
         * part.getContentType() + ".</br>"); out.println("文件名为：" + filename +
         * "</br>");
         */
    }
}

注释比较详细，就不仔细介绍了

里面的异步任务实际上是启动了一个runnable对象，接下来是这个类的内容

package liujie.jee.bean;

import java.io.IOException;

import javax.servlet.AsyncContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.Part;

public class UploadFileExecutor implements Runnable {
    private AsyncContext asct;
    private Part part;
    private final static String UPLODA_DIR = "z_uploadfiles";

    public UploadFileExecutor(AsyncContext asct) {
        this.asct = asct;
    }

    @Override
    public void run() {
        HttpServletRequest request = (HttpServletRequest) asct.getRequest();
        String fileName = request.getParameter("name");
        try {
            // 获取上传的对象
            Part part = request.getPart("file");
            // 获取保存的路径并将文件吸入改路径
            part.write(request.getServletContext().getRealPath(UPLODA_DIR)
                    + "\\" + fileName);
            // 完成调用
            asct.complete();
        } catch (IllegalStateException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ServletException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

注意要在应用根目录下面建立一个z_uploadfiles的目录放文件

JavaEE拾遗01--异步上传文件

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