java中struts2实现简单的文件上传与下载
一、struts2文件上传
struts2的文件上传实现非常简单,只需要简单几步就可完成;
注意:
(1)文件上传的struts2标签为:<s:file name="" label="上传"/>
(2)文件上传的前提是表单属性method="post" enctype="multipart/form-data";
(3)web应用中必须包含common-fileupload.jar和common-io.jar,因为struts2默认上传解析器使用的是jakarta;
(4)可以在struts.xml中配置最大允许上传的文件大小:<constant name="struts.multipart.maxsize" value="....."/>,默认为2m;
1.普通文件上传
实现规则:
(1)在jsp中设定表单控件<s:file name="upload" label="上传"/>
(2)在action中定义属性:
private file upload; //包含文件内容
private string uploadfilename; //上传文件的名称;
private string uploadcontenttype; //上传文件的mime类型;
这些属性都会随着文件的上传自动赋值;
(3)在execute()中完成写入磁盘功能;
代码示例:
upload01action.java
package org.upload.action; import java.io.file; import java.io.fileinputstream; import java.io.fileoutputstream; import org.apache.struts2.servletactioncontext; import com.opensymphony.xwork2.actionsupport; public class upload01action extends actionsupport { private file upload; private string uploadfilename; private string uploadcontenttype; private string name; public string execute()throws exception{ string path = servletactioncontext.getservletcontext().getrealpath("/web-inf/upload"); string filename = path+file.separator+name; fileinputstream in = new fileinputstream(upload); fileoutputstream out = new fileoutputstream(filename); byte[]b = new byte[1024]; int len = 0; while((len=in.read(b))>0){ out.write(b,0,len); } out.close(); return success; } public file getupload() { return upload; } public void setupload(file upload) { this.upload = upload; } public string getuploadfilename() { return uploadfilename; } public void setuploadfilename(string uploadfilename) { this.uploadfilename = uploadfilename; } public string getuploadcontenttype() { return uploadcontenttype; } public void setuploadcontenttype(string uploadcontenttype) { this.uploadcontenttype = uploadcontenttype; } public string getname() { return name; } public void setname(string name) { this.name = name; } }
struts.xml
<?xml version="1.0" encoding="utf-8" ?> <!doctype struts public "-//apache software foundation//dtd struts configuration 2.0//en" "http://struts.apache.org/dtds/struts-2.0.dtd"> <struts> <constant name="struts.devmode" value="true" /> <constant name="struts.custom.i18n.resources" value="message"></constant> <package name="default" namespace="/" extends="struts-default"> <action name="upload0*" class="org.upload.action.upload0{1}action"> <param name="name">1.jpg</param> <result>/{1}.jsp</result> </action> </package> </struts>
1.jsp
<%@ page language="java" import="java.util.*" pageencoding="utf-8"%> <%@taglib prefix="s" uri="/struts-tags" %> <!doctype html public "-//w3c//dtd html 4.01 transitional//en"> <html> <head> <title>my jsp '1.jsp' starting page</title> </head> <body> <s:form action="upload01" method="post" enctype="multipart/form-data"> <s:file name="upload" label="上传"></s:file> <s:submit value="上传"></s:submit> </s:form> </body> </html>
2.利用拦截器进行过滤
手动实现过滤的方式非常简单,就是利用输入校验的方式进行过滤,即在validate()中进行过滤;
而这里要讲的拦截器方式是很好的方式,只需要在配置文件中配置,灵活性很好,能够限制文件的类型、文件的大小;如果上传的文件不符合要求,则返回input逻辑视图;
配置拦截器步骤:
(1)文件上传的拦截器为fileupload;
(2)需要给定参数allowedtypes、maximumsize;
(3)在fileupload拦截器后,需要添加<interceptor-ref name="defaultstack"/>
代码示例:
由于通过拦截器进行过滤只需要配置struts.xml,因此这里只给出struts.xml的配置
<?xml version="1.0" encoding="utf-8" ?> <!doctype struts public "-//apache software foundation//dtd struts configuration 2.0//en" "http://struts.apache.org/dtds/struts-2.0.dtd"> <struts> <constant name="struts.devmode" value="true" /> <constant name="struts.custom.i18n.resources" value="message"></constant> <package name="default" namespace="/" extends="struts-default"> <action name="upload0*" class="org.upload.action.upload0{1}action"> <interceptor-ref name="fileupload"> <param name="allowedtypes">image/jpeg,image/gif</param> <param name="maximumsize">1024*1024</param> </interceptor-ref> <interceptor-ref name="defaultstack"></interceptor-ref> <param name="name">1.jpg</param> <result>/{1}.jsp</result> <result name="input">/{1}.jsp</result> </action> </package> </struts>
我们还需要配置文件上传失败后的错误提示信息,我们需要在全局国际化资源文件中配置:
struts.messages.error.content.type.not.allowed=文件类型不匹配 struts.messages.error.file.too.large=文件太大
二、struts2文件下载
我们在学习servlet和http协议时已经可以实现文件下载,即写content-disposition头即可,struts2的实现原理也是这个,但是提供了更好的封装性;
struts2的stream结果类型专门用于实现文件下载;
(1)struts.xml中配置stream结果类型,并配置contenttype、contentdisposition、buffersize参数即可,模板:
<action name="download" class=""> <result type="stream" name="success"> <param name="contenttype"></param> <param name="contentdisposition">attachment;filename=""</param> <param name="buffersize">4096</param> </result> </action>
(2)在action中创建public inputstream getinputstream()throws exception;方法,此方法用于获得下载文件的输入流;
downloadaction.java
package org.download.action; import java.io.inputstream; import org.apache.struts2.servletactioncontext; import com.opensymphony.xwork2.actionsupport; public class downloadaction extends actionsupport { public inputstream getinputstream()throws exception{ return servletactioncontext.getservletcontext().getresourceasstream("/web-inf/upload/1.jpg"); } public string execute()throws exception{ return success; } }
struts.xml
<action name="download" class="org.download.action.downloadaction"> <result type="stream" name="success"> <param name="contenttype">image/jpeg</param> <param name="contentdisposition">attachment;filename="1.jpg"</param> <param name="buffersize">4096</param> </result> </action>
就可以完成下载。
java中struts2文件上传下载的实现就为大家介绍到这里,谢谢大家的阅读。
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