1.实现原理：
在大文件上传时显示上传进度是很有必要的，不能让用户感觉到陷入无穷的等待中，或感觉程序已经卡死。为此我们可以在session中存一个上传进度的变量，在文件上传的过程中实时的去修改这个值，这就需要在后台重写Spring MVC自带的上传解析类，每上传一定的字节数就修改一下session中的进度，在前台通个AJAX请求每隔一定的时间去获取这个值显示给用户，这样就达到了显示上传进度的需求，不过这样频繁的请求服务器无疑是增加了服务器的压力，在没有使用任何第三方上传组件的情况下只能如此。
2.测试结果：
没有出现任何内存溢出或奔溃的情况。
前台效果和后台打印日志:
3.代码
①CustomMultipartResolver.java,Spring默认的文件上传类是CommonsMultipartResolver,我们需要自定义一个类CustomMultipartResolver继承它.
package com.upload;
import java.util.List;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.FileUpload;
import org.apache.commons.fileupload.FileUploadBase;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.springframework.web.multipart.MaxUploadSizeExceededException;
import org.springframework.web.multipart.MultipartException;
import org.springframework.web.multipart.MultipartHttpServletRequest;
import org.springframework.web.multipart.commons.CommonsMultipartResolver;
public class CustomMultipartResolver extends CommonsMultipartResolver {
private HttpServletRequest request;
protected FileUpload newFileUpload(FileItemFactory fileItemFactory) {
ServletFileUpload upload = new ServletFileUpload(fileItemFactory);
if (request != null) {
HttpSession session = request.getSession();
MyProgressListener uploadProgressListener = new MyProgressListener(session);
upload.setProgressListener(uploadProgressListener);
}
return upload;
}
public MultipartHttpServletRequest resolveMultipart(
HttpServletRequest request) throws MultipartException {
this.request = request;// 获取到request,要用到session
return super.resolveMultipart(request);
}
@Override
public MultipartParsingResult parseRequest(HttpServletRequest request)
throws MultipartException {
String encoding = determineEncoding(request);
FileUpload fileUpload = prepareFileUpload(encoding);
//设置监听器
MyProgressListener progressListener = new MyProgressListener(request.getSession());
fileUpload.setProgressListener(progressListener);
try {
List<FileItem> fileItems = ((ServletFileUpload) fileUpload).parseRequest(request);
return parseFileItems(fileItems, encoding);
}
catch (FileUploadBase.SizeLimitExceededException ex) {
throw new MaxUploadSizeExceededException(fileUpload.getSizeMax(), ex);
}
catch (FileUploadException ex) {
throw new MultipartException("Could not parse multipart servlet request", ex);
}
}
}
②spring-servlet.xml,XML配置
<!-- 文件上传配置 -->
<!-- <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
<property name="maxUploadSize" value="1048576000"/>
<property name="maxInMemorySize" value="4096"/>
<property name="defaultEncoding" value="UTF-8"></property>
</bean>
-->
<bean id="multipartResolver" class="com.upload.CustomMultipartResolver">
<property name="maxUploadSize" value="1048576000"/>
<property name="maxInMemorySize" value="4096"/>
<property name="defaultEncoding" value="UTF-8"></property>
</bean>
③MyProgressListener.java,文件上传监听器,需要实现ProgressListener接口
package com.upload;
import javax.servlet.http.HttpSession;
import org.apache.commons.fileupload.ProgressListener;
public class MyProgressListener implements ProgressListener {
private HttpSession session;
public MyProgressListener() {
}
public MyProgressListener(HttpSession session) {
this.session = session;
ProgressEntity ps = new ProgressEntity();
session.setAttribute("upload_ps", ps);
}
public void setSession(HttpSession session){
this.session = session;
}
@Override
public void update(long pBytesRead, long pContentLength, int pItems) {
ProgressEntity ps = (ProgressEntity) session.getAttribute("upload_ps");
ps.setpBytesRead(pBytesRead);
ps.setpContentLength(pContentLength);
ps.setpItems(pItems);
//更新
session.setAttribute("upload_ps", ps);
// System.out.println("当前进度:"+ps.getpBytesRead());
}
}
④ProgressEntity.java 包含上传信息的实体
package com.upload;
public class ProgressEntity {
private long pBytesRead = 0L; //到目前为止读取文件的比特数
private long pContentLength = 0L; //文件总大小
private int pItems; //目前正在读取第几个文件
public long getpBytesRead() {
return pBytesRead;
}
public void setpBytesRead(long pBytesRead) {
this.pBytesRead = pBytesRead;
}
public long getpContentLength() {
return pContentLength;
}
public void setpContentLength(long pContentLength) {
this.pContentLength = pContentLength;
}
public int getpItems() {
return pItems;
}
public void setpItems(int pItems) {
this.pItems = pItems;
}
@Override
public String toString() {
return "ProgressEntity [pBytesRead=" + pBytesRead + ", pContentLength="
+ pContentLength + ", pItems=" + pItems + "]";
}
}
⑤Action中的方法,上传方法任然不用变，还是原来的Spring上传方法，只需修改XML中的上传解析器.改成前面自定义的即可，增加一个获取上传进度的方法。SuccessBean是封装了返回前台的信息：包含success和msg两个字段。
@ResponseBody
@RequestMapping(value = "/getProgress", method = RequestMethod.GET)
public SuccessBean getProgress(HttpServletRequest request, HttpServletResponse response){
if(request.getSession().getAttribute("upload_ps")==null){
return new SuccessBean(true,"0");
}
ProgressEntity ps = (ProgressEntity)request.getSession().getAttribute("upload_ps");
Double percent = 0d;
if(ps.getpContentLength() != 0L){
percent = (double)ps.getpBytesRead()/(double)ps.getpContentLength()*1.0d; //百分比
if(percent != 0d){
DecimalFormat df = new DecimalFormat("0.00");
percent = Double.parseDouble(df.format(percent));
}
}
logger.info("当前上传进度:" + percent.toString());
return new SuccessBean(true, percent.toString());
}
⑥前台就更简单了，只需一个FormPanel添加一个filefield组件,在表单提交后同时启动定时任务，每隔1秒从后台获取一下进度显示出来即可。
时间： 2024-10-11 16:45:54