JavaServlet的文件上传和下载实现方法

先分析一下上传文件的流程

1-先通过前段页面中的选择文件选择要上传的图片

index.jsp

<%@ page language=\”java\” import=\”java.util.*\” pageEncoding=\”utf-8\”
contentType=\”text/html; charset=UTF-8\”%>

<!DOCTYPE HTML PUBLIC \”-//W3C//DTD HTML 4.01 Transitional//EN\”>
<html>
<head>
<title>My JSP \’index.jsp\’ starting page</title>
<meta http-equiv=\”content-type\” content=\”text/html;charset=utf-8\”>
<meta http-equiv=\”pragma\” content=\”no-cache\”>
<meta http-equiv=\”cache-control\” content=\”no-cache\”>
<meta http-equiv=\”expires\” content=\”0\”>
<meta http-equiv=\”keywords\” content=\”keyword1,keyword2,keyword3\”>
<meta http-equiv=\”description\” content=\”This is my page\”>

2-点击提交按钮，通过ajax的文件上传访问服务器端

common.js　　

var path = (function() {
//获取当前网址
var curWwwPath = window.document.location.href;
//获取主机地址之后的目录
var pathName = window.document.location.pathname;
var pos = curWwwPath.indexOf(pathName);
//获取主机地址
var localhostPath = curWwwPath.substring(0, pos);
//获取带\”/\”的项目名
var projectName = pathName.substring(0, pathName.substr(1).indexOf(\’/\’) + 1);
return {
curWwwPath: curWwwPath,
pathName: pathName,
localhostPath: localhostPath,
projectName: projectName,
//部署路径
deployPath: localhostPath + projectName
};
})();

// 文件下载
$(\”a[id=downLoad]\”).click(function(){
window.location.href=path.deployPath+\”/fileDown\”;
});
// 文件上传
$(\”input[id=upload]\”).click(function() {
$.ajaxFileUpload( {
url : path.deployPath + \”/fileUp\”, // 处理页面的绝对路径
fileElementId : \”inputImage\”, //file空间的id属性
dataType : \”json\”,
success : function(data) {
alert(\”上传成功\”);
}
});
});

3-服务器端响应保存或者下载

保存上传文件的FileUpload.java

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import net.sf.json.JSONArray;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import com.stu.util.HttpUtil;
/**
* 文件名称： com.stu.fileupload.FileUpload.java 
* 初始作者： Administrator 
* 创建日期： 2018-1-31 
* 功能说明：文件上传 
* ================================================= 
* 修改记录： 
* 修改作者日期修改内容 
* ================================================ 
* Copyright (c) 2010-2011 .All rights reserved. 
*/
public class FileUpload extends HttpServlet {
private static final long serialVersionUID = 1L;
@Override
protected void service(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
// 获取到当前服务器所在的路径
String serverPath = req.getSession().getServletContext().getRealPath(\”/\”);
// 设置保存上传文件的路径
String saveDirPath = serverPath + \”img\”;
File saveDirPathFileObj = new File(saveDirPath);
// 如果当用来存放文件的目录不存在时，要创建该目录
if (!saveDirPathFileObj.exists()) {
saveDirPathFileObj.mkdirs();
}
// 创建一个解析器工厂
DiskFileItemFactory factory = new DiskFileItemFactory();
// 设置工厂的缓存区大小
factory.setSizeThreshold(5 * 1024);
// 文件上传的解析器(文件上传对象)
ServletFileUpload upload = new ServletFileUpload(factory);
// 设置上传文件的最大值
upload.setSizeMax(3 * 1024 * 1024);
// 设置编码格式
upload.setHeaderEncoding(\”UTF-8\”);
try {
// 上传以后的文件名
List<String> uploadFileNames = new ArrayList<String>();
List<FileItem> fileItems = upload.parseRequest(req);
System.out.println(fileItems);
for (FileItem file : fileItems) {
// 新的文件名
String saveFileName = UUID.randomUUID().toString().replace(\”-\”, \”\”);
// 文件的后缀
String oldFileName = new String(file.getName().getBytes(),
\”UTF-8\”);
System.out.println(\”oldFileName\” + oldFileName);
String fileType = oldFileName.substring(oldFileName.lastIndexOf(\”.\”));
// 新的文件路径
String saveFilePath = saveDirPath + File.separator
+ saveFileName + fileType;
uploadFileNames.add(saveFileName + fileType);
// 保存上传的文件
file.write(new File(saveFilePath));
}
System.out.println(uploadFileNames);
HttpUtil.setAttribute(req, \”urls\”, uploadFileNames);
res.setContentType(\”application/json;charset=utf-8\”);
PrintWriter pw = res.getWriter();
pw.print(JSONArray.fromObject(uploadFileNames));
} catch (FileUploadException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
}

下载文件的FileDownload.java

这里面用到了一个HttpUtil类，代码如下：

import javax.servlet.FilterConfig;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
/**
* 文件名称＿com.niit.model2.util.Httputil.java
* 初始作逯ܿAdministrator
* 创建日期＿2018-1-23
* 功能说明＿这里用一句话描述这个类的作用–此句话需删除 
* ================================================= 
* 修改记录＿br/>
* 修改作迠日期修改内容 
* ================================================ 
* Copyright (c) 2010-2011 .All rights reserved. 
*/
public class HttpUtil {
private HttpUtil() {
}
/**
* 方法描述: [用于向不同的作用域存放属性]
* 初始作迺 Administrator 
* 创建日期: 2018-1-23-上午11:24:45 
* 弿ǋ版本: 2.0.0 
* ================================================= 
* 修改记录＿br/>
* 修改作迠日期修改内容 
* ================================================ 
* void
*/
public static void setAttribute(Object scopeObj, String name, Object value) {
if (scopeObj instanceof HttpServletRequest) {
((HttpServletRequest) scopeObj).setAttribute(name, value);
}
if (scopeObj instanceof HttpSession) {
((HttpSession) scopeObj).setAttribute(name, value);
}
if (scopeObj instanceof ServletContext) {
((ServletContext) scopeObj).setAttribute(name, value);
}
}
/**
* 方法描述: [获取作用域中指定名称的属性思
* 初始作迺 Administrator 
* 创建日期: 2018-1-23-上午11:29:17 
* 弿ǋ版本: 2.0.0 
* ================================================= 
* 修改记录＿br/>
* 修改作迠日期修改内容 
* ================================================ 
*
* @param scopeObj
* @param name
* @return
* Object
*/
public static Object getAttribute(Object scopeObj, String name) {
if (scopeObj instanceof HttpServletRequest) {
return ((HttpServletRequest) scopeObj).getAttribute(name);
}
if (scopeObj instanceof HttpSession) {
return ((HttpSession) scopeObj).getAttribute(name);
}
if (scopeObj instanceof ServletContext) {
return ((ServletContext) scopeObj).getAttribute(name);
}
return null;
}
/**
* 方法描述: [获取上下文对象的方法]
* 初始作迺 Administrator 
* 创建日期: 2018-1-23-上午11:31:26 
* 弿ǋ版本: 2.0.0 
* ================================================= 
* 修改记录＿br/>
* 修改作迠日期修改内容 
* ================================================ 
*
* @return
* ServletContext
*/
public static ServletContext getServletContext(Object sourceObj) {
if (sourceObj instanceof HttpServletRequest) {
return ((HttpServletRequest) sourceObj).getSession().getServletContext();
}
if (sourceObj instanceof ServletConfig) {
return ((ServletConfig) sourceObj).getServletContext();
}
if (sourceObj instanceof FilterConfig) {
return ((FilterConfig) sourceObj).getServletContext();
}
return null;
}
/**
* 方法描述: [获取项目的实际路径]
* 初始作迺 Administrator 
* 创建日期: 2018-1-23-上午11:45:47 
* 弿ǋ版本: 2.0.0 
* ================================================= 
* 修改记录＿br/>
* 修改作迠日期修改内容 
* ================================================ 
*
* @param req
* @return
* String
*/
public static String getContextPath(HttpServletRequest req) {
return req.getContextPath();
}
}

当然，代码编辑好了也不要忘了在 WebRoot/WEB-INF/web.xml 中添加新建的Servlet，就是刚刚的两个Java文件啦

<?xml version=\”1.0\” encoding=\”UTF-8\”?>
<web-app version=\”2.5\” xmlns=\”http://java.sun.com/xml/ns/javaee\”
xmlns:xsi=\”wp-content/uploads/2023/12/XMLSchema-instance\”
xsi:schemaLocation=\”http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd\”>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<!– 文件上传 –>
<servlet>
<servlet-name>fileUpload</servlet-name>
<servlet-class>com.stu.fileupload.FileUpload</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>fileUpload</servlet-name>
<url-pattern>/fileUp</url-pattern>
</servlet-mapping>
<!– 文件下载 –>
<servlet>
<servlet-name>fileDownload</servlet-name>
<servlet-class>com.stu.fileupload.FileDownload</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>fileDownload</servlet-name>
<url-pattern>/fileDown</url-pattern>
</servlet-mapping>
</web-app>