JavaServlet的文件上传和下载实现方法（导入servlet-api.jar包）奔走相告

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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=https://www.jb51.net/article/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;

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;

public class HttpUtil {
private HttpUtil() {
}

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);
}
}

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;
}

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;
}

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=”http://www.w3.org/2001/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>

这样的话就可以运行啦。

TIP：不要忘记相关的jar包和 js 包哦

在 WebRoot / WEB-INF / lib 下，有 commons-fileupload.jar 和 commons-io.jar ，另外 json-lib-x.x.x-jdkxx.jar 包是用来把上传的返回数据修改为JSON格式的

在 WebRoot / js 下，导入 jquery.js , common.js , ajaxfileupload.js

以上这篇JavaServlet的文件上传和下载实现方法就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持脚本之家。

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