struts2 文件上传 和部分源码解析，以及一般上传原理
（1） 单文件上传
一.简介
Struts2并未提供自己的请求解析器，也就是就Struts2不会自己去处理multipart/form-data的请求，它需要调用其他请求解析器，将HTTP请求中的表单域解析出来。但Struts2在原有的上传解析器基础
上做了进一步封装，更进一步简化了文件上传。
Struts2默认使用的是Jakarta的Common-FileUpload框架来上传文件，因此，要在web应用中增加两个Jar文件：commons-fileupload-1.2.jar和commons-io-1.3.1.jar。它在原上传框架上做了进一步封装
，简化了文件上传的代码实现，取消了不同上传框架上的编程差异。
如果要改成其它的文件上传框架，可以修改struts.multipart.parser常量的值为cos/pell，默认值是jakata。并在classpath中增加相应上传组件的类库
例如配置成cos上传
struts.multipart.parser=cos
struts.multipart.maxSize=1024 指定文件的最大字结数
二.原理
不管用common-fileUPload框架，还是用cos，都是通过将HTTP的数据保存到临时文件夹，然后Struts使用fileUpload拦截器将文件绑定到Action的实例中。
也就是配置文件的 <interceptor-ref name="fileUpload"/>
我们可以通过源代码struts2-code-XX.jar的struts-default.xml文件找到
<interceptor name="fileUpload" class="org.apache.struts2.interceptor.FileUploadInterceptor"/>
打开这个类的源代码可以看见相关如下：
/**
* <!-- START SNIPPET: description -->
* <p/>
* Interceptor that is based off of {@link MultiPartRequestWrapper}, which is automatically applied for any request that
* includes a file. It adds the following parameters, where [File Name] is the name given to the file uploaded by the
* HTML form:
* <p/>
* <ul>
* <p/>
* <li>[File Name] : File - the actual File</li>
* <p/>
* <li>[File Name]ContentType : String - the content type of the file</li>
* <p/>
* <li>[File Name]FileName : String - the actual name of the file uploaded (not the HTML name)</li>
* <p/>
* </ul>
* <p/>
也就是说我们需要三个变量File（表单的name），其他两个参数通过set个体方法有strtus调用
接着下面是一些国际化提示的东西：
* processed for all i18n requests. You can override the text of these messages by providing text for the following
* keys:
* <li>struts.messages.error.uploading - a general error that occurs when the file could not be uploaded</li>
* <p/>
* <li>struts.messages.error.file.too.large - occurs when the uploaded file is too large</li>
* <p/>
* <li>struts.messages.error.content.type.not.allowed - occurs when the uploaded file does not match the expected
* content types specified</li>
* <p/>
* <li>struts.messages.error.file.extension.not.allowed - occurs when the uploaded file does not match the expected
* file extensions specified</li>
* <p/>
例如struts.messages.error.content.type.not.allowed 表示文件类型错误：也就是说如果我们给拦截器配置了属性allowedTypes 例如：
<param name ="allowedTypes">image/bmp,image/png,image/gif,image/jpeg,image/jpg</param> 但是上传的时候没有上传规定的类型
struts2就会去我们的资源文件去找key为struts.messages.error.content.type.not.allowed的国际化资源给与提示这时候我们可以在我们的资源中配置这个key：
例如：struts.messages.error.content.type.not.allowed=您上传的文件类型只能为...！请重新选择！
(当然需要<constant name="struts.custom.i18n.resources" value="globalMessages"/>)globalMessages为资源前缀，然后通过：<s:fielderror/>来显示提示
<!-- START SNIPPET: parameters -->
* <p/>
* <ul>
* <p/>
* <li>maximumSize (optional) - the maximum size (in bytes) that the interceptor will allow a file reference to be set
* on the action. Note, this is <b>not</b> related to the various properties found in struts.properties.
* Default to approximately 2MB.</li>
* <p/>
* <li>allowedTypes (optional) - a comma separated list of content types (ie: text/html) that the interceptor will allow
* a file reference to be set on the action. If none is specified allow all types to be uploaded.</li>
* <p/>
* <li>allowedExtensions (optional) - a comma separated list of file extensions (ie: .html) that the interceptor will allow
* a file reference to be set on the action. If none is specified allow all extensions to be uploaded.</li>
* </ul>
* <p/>
上面则是拦截器的相关参数，一目了然：maximumSize 上传文件最大多少 默认：2MB。allowedTypes容许的上传类型。allowedExtensions容许的扩展名
接着是相关action的代码说明：
<!-- START SNIPPET: example-action -->
* package com.example;
* <p/>
* import java.io.File;
* import com.opensymphony.xwork2.ActionSupport;
* <p/>
* public UploadAction extends ActionSupport {
* private File file;
* private String contentType;
* private String filename;
* <p/>
* public void setUpload(File file) {
* this.file = file;
* }
* <p/>
* public void setUploadContentType(String contentType) {
* this.contentType = contentType;
* }
* <p/>
* public void setUploadFileName(String filename) {
* this.filename = filename;
* }
* <p/>
* public String execute() {
* //...
* return SUCCESS;
* }
* }
其实最主要的是set方法的确定：我们跟踪到大约238行：
String contentTypeName = inputName + "ContentType";
String fileNameName = inputName + "FileName";
最终确定我们的private File file;属性名称可以随便，
但是filenam和contenttype的set方法要有规定 例如：
如果private File myFile;
则对应的其他的两个属性set方法如下：
public void setMyFileContentType(String contentType) {
this.contentType = contentType;//当然contentType可以随便起名 最终要的是set+MyFile+ContentType方法
}
public void setMyFileFileName(String filename) {
this.filename = filename;/当然filename可以随便起名 最终要的是set+MyFile+FileName方法
}
以下是实例：
三.需要的jar包(默认使用commons-fileupload,如果使用cos，要将jar引进来)
commons-logging-1.1.jar
freemarker-2.3.8.jar
ognl-2.6.11.jar
struts2-core-2.0.6.jar
xwork-2.0.1.jar
commons-io-1.3.1.jar
commons-fileupload-1.2.jar
四.实例
1.首先，创建上传页面
Html代码
1.<%@page language="java" contentType = "text/html; charset=utf-8" pageEncoding = "utf-8"%>
2.<%@taglib prefix="s" uri ="/struts-tags"%>
3.
4.<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
5.<html>
6. <head>
19. </head>
20.
21. <body>
22. <s:form action ="fileUpload" method ="POST" enctype ="multipart/form-data">
23. <s:fielderror />
24. <s:file name ="upload"/>
25. <s:submit />
26. </s:form >
27.
28. </body>
29.</html>
2.action
1.package com;
2.
3.import java.io.BufferedInputStream;
4.import java.io.BufferedOutputStream;
5.import java.io.File;
6.import java.io.FileInputStream;
7.import java.io.FileOutputStream;
8.import java.io.InputStream;
9.import java.io.OutputStream;
10.import java.util.Date;
11.
12.import org.apache.struts2.ServletActionContext;
13.
14.import com.opensymphony.xwork2.ActionSupport;
15.
16.public class FileUploadAction extends ActionSupport {
17.
18. private static final long serialVersionUID = 6452146812454l;
19.
20. private File upload;
21.
22. private String uploadContentType;
23.
24. private String uploadFileName;
25.
26. private String imageFileName;
27.
28. public String getUploadContentType() {
29. return uploadContentType;
30. }
31.
32. public void setUploadContentType(String uploadContentType) {
33. this.uploadContentType = uploadContentType;
34. }
35.
36. public File getUpload() {
37. return upload;
38. }
39.
40. public void setUpload(File upload) {
41. this.upload = upload;
42. }
43.
44. public String getUploadFileName() {
45. return uploadFileName;
46. }
47.
48. public void setUploadFileName(String uploadFileName) {
49. this.uploadFileName = uploadFileName;
50. }
51.
52. public void setImageFileName(String imageFileName) {
53. this.imageFileName = imageFileName;
54. }
55.
56. public String getImageFileName() {
57. return imageFileName;
58. }
59.
60. private static void copy(File src, File dst) {
61. try {
62. InputStream in = null;
63. OutputStream out = null;
64. try {
65. in = new BufferedInputStream(new FileInputStream(src));
66. out = new BufferedOutputStream(new FileOutputStream(dst));
67. byte[] buffer = new byte[1024*10];
68. while (in.read(buffer) > 0) {
69. out.write(buffer);
70. }
71. } finally {
72. if (null != in) {
73. in.close();
74. }
75. if (null != out) {
76. out.close();
77. }
78. }
79. } catch (Exception e) {
80. e.printStackTrace();
81. }
82. }
83.
84. @Override
85. public String execute() {
86. System.out.println(uploadFileName);
87.
88. imageFileName = System.currentTimeMillis() + uploadFileName.substring(uploadFileName.lastIndexOf("."));
89. File imageFile = new File(ServletActionContext.getServletContext()
90. .getRealPath("/uploadImages")
91. + "/" + imageFileName); //我们自己重新定义的文件名，也可以直接用 uploadFileName
92. copy(upload, imageFile);
93. return SUCCESS;
94. }
95.
96.}
97
表单的enctype ="multipart/form-data，与一般的上传一样．
<s:file name="upload">会将upload绑定到action的upload,其次他还会将上传记文件的MIME类型绑定到uploadContentType,文件名绑定到uploadFileName中，他们是通过
setUploadContentType和setUploadFileName进行绑定的,下面进行的多文件上传也是同个道理，不过要用数组或者是list来进行绑定，然后多个文件的MIME类型也会绑定到以数组
名字加ContentType和FileName的字符串数组中。 比如说上传的文件的数组名为：File[] uploads,则它们的MIME类型绑定的对应的数组是uploadsFileName和uploadsContentType.
3.struts.xml的配置
Xml代码
Xml代码
1.<?xml version="1.0" encoding="UTF-8" ?>
2.<!DOCTYPE struts PUBLIC
3. "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
4. "http://struts.apache.org/dtds/struts-2.0.dtd">
5.
6.<struts>
7. <constant name="struts.multipart.saveDir" value="/tmp" />
8. <package name="fileUploadDemo" extends="struts-default">
9. <action name ="fileUpload" class ="com.FileUploadAction">
10.
11. <interceptor-ref name ="fileUpload">
12. <param name ="allowedTypes">image/bmp,image/png,image/gif,image/jpeg,image/jpg</param>
13. </interceptor-ref>
14. <interceptor-ref name ="defaultStack"/>
15.
16. <result name ="input" >/fileUpload.jsp</result>
17. <result name ="success">/showUpload.jsp </result>
18. </action>
19. </package>
20.</struts>
4.最后是web.xml的配置
Xml代码
1.<?xml version="1.0" encoding="UTF-8"?>
2.<web-app version="2.4"
3. xmlns="http://java.sun.com/xml/ns/j2ee"
4. xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
5. xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
6. http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
7.
8. <filter>
9. <filter-name>struts-cleanup</filter-name>
10. <filter-class>
11. org.apache.struts2.dispatcher.ActionContextCleanUp
12. </filter-class>
13. </filter>
14.
15. <filter>
16. <filter-name>struts2</filter-name >
17. <filter-class>
18. org.apache.struts2.dispatcher.FilterDispatcher
19. </filter-class >
20. </filter>
21.
22. <filter-mapping>
23. <filter-name>struts-cleanup</filter-name >
24. <url-pattern>/*</url-pattern>
25. </filter-mapping>
26.
27. <filter-mapping>
28. <filter-name>struts2</filter-name >
29. <url-pattern>/*</url-pattern >
30. </filter-mapping>
31.
32. <welcome-file-list>
33. <welcome-file>index.jsp</welcome-file>
34. </welcome-file-list>
35.</web-app>
（2） 多文件上传
多文件上传
与单文件上传相似，实现多文件你可以将多个<s:file />绑定Action的数组或列表。如下例所示。
< s:form action ="uploadList" method ="POST" enctype ="multipart/form-data" >
< s:file label ="File (1)" name ="upload" />
< s:file label ="File (2)" name ="upload" />
< s:file label ="FIle (3)" name ="upload" />
< s:submit />
</ s:form > 清单14 多文件上传JSP代码片段
如果你希望绑定到数组，Action的代码应类似：
private File[] uploads;
private String[] uploadSFileName;
private String[] uploadSContentType;
多文件上传数组绑定Action代码片段
如果你想绑定到列表，则应类似：
private List < File > uploads ;
private List < String > uploadSFileName ;
private List < String > uploadSContentType ;
多文件上传列表绑定Action代码片段
另外是一般上传文件的原理：当然具体可以看http协议的rfc文档：
关于multipart/form-data 相关资料可以看;http://www.ietf.org/rfc/rfc1867.txt 大约在[Page 1]的地方有介绍
表单配置multipart/form-data 说明以二进制流的方式传输表单字段的数据：
我们通过以下代码看到request数据流中的内容：
PrintWriter out = response.getWriter();
InputStream is = request.getInputStream();
BufferedReader br = new BufferedReader(
new InputStreamReader(is));
String buffer = null;
while( (buffer = br.readLine()) != null)
{
//在页面中显示读取到的请求参数
out.println(buffer + "<br />");
}
out.flush();
out.close();
例如：我上传一个文件D:\apache-tomcat-6018\bin\version.sh （tomcat版本文件）
最终页面显示：
-----------------------------7da1052ec05fe
Content-Disposition: form-data; name="ff"; filename="D:\apache-tomcat-6018\bin\version.sh"
Content-Type: text/plain
#!/bin/sh
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements. See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# resolve links - $0 may be a softlink
PRG="$0"
while [ -h "$PRG" ] ; do
ls=`ls -ld "$PRG"`
link=`expr "$ls" : '.*-> \(.*\)$'`
if expr "$link" : '/.*' > /dev/null; then
PRG="$link"
else
PRG=`dirname "$PRG"`/"$link"
fi
done
PRGDIR=`dirname "$PRG"`
EXECUTABLE=catalina.sh
# Check that target executable exists
if [ ! -x "$PRGDIR"/"$EXECUTABLE" ]; then
echo "Cannot find $PRGDIR/$EXECUTABLE"
echo "This file is needed to run this program"
exit 1
fi
exec "$PRGDIR"/"$EXECUTABLE" version "$@"
-----------------------------7da1052ec05fe--
我们发现我们上传的内容在
-----------------------------7da1052ec05fe
Content-Disposition: form-data; name="ff"; filename="D:\apache-tomcat-6018\bin\version.sh"
Content-Type: text/plain和-----------------------------7da1052ec05fe--中间
因此我们可以通过以下代码来获取上传内容并保存：
//取得HttpServletRequest的InputStream输入流
InputStream is = request.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(is));
String buffer = null;
//循环读取请求内容的每一行内容
while( (buffer = br.readLine()) != null)
{
//如果读到的内容以-----------------------------开始，
//且以--结束，表明已到请求内容尾
if(buffer.endsWith("--") && buffer
.startsWith("-----------------------------"))//length为29
{
//跳出循环
break;
}
//如果读到的内容以-----------------------------开始，表明开始了一个表单域
if(buffer.startsWith("-----------------------------"))
{
//如果下一行内容中有filename字符串，表明这是一个文件域
if (br.readLine().indexOf("filename") > 1)
{
//跳过两行，开始处理上传的文件内容
br.readLine();
br.readLine();
//以系统时间为文件名，创建一个新文件
File file = new File(request.getRealPath("/")
+ System.currentTimeMillis());
//当然我们可以读取filenam来保存这里简化
//创建一个文件输出流
PrintStream ps = new PrintStream(new FileOutputStream(file));
String content = null;
//接着开始读取文件内容
while( (content = br.readLine()) != null)
{
//如果读取的内容以-----------------------------开始，
//表明开始了下一个表单域内容
if(content.startsWith("-----------------------------"))length为29
{
//跳出处理
break;
}
//将读到的内容输出到文件中
ps.println(content);
}
//关闭输出
ps.flush();
ps.close();
}
}
}
br.close();
关于strtus2下载:
下载最终是通过contentType和数据流将数据输出到客户端来实现，在struts中也是通过InputStream和相关的配置来实现：
同样最终到strtus的下载相关的源代码：org.apache.struts2.dispatcher.StreamResult我们看到
public static final String DEFAULT_PARAM = "inputName";
protected String contentType = "text/plain";
protected String contentLength;
protected String contentDisposition = "inline";//在线
protected String contentCharSet ;
protected String inputName = "inputStream";
protected InputStream inputStream;
protected int bufferSize = 1024;
protected boolean allowCaching = true;
当然这些参数都可以在 <result type="stream">中配置 例如;
<param name="inputPath">\uploads\document.pdf</param>
<!-- 指定下载文件的文件类型 -->
<param name="contentType">Application/pdf</param>
<!-- 指定由getTargetFile()方法返回被下载文件的InputStream -->
<param name="inputName">targetFile</param>
<param name="contentDisposition">attachment;filename="document.pdf"</param>
<!-- 指定下载文件的缓冲大小 -->
<param name="bufferSize">2048</param>
其中：
contentType：指定被下载文件的文件类型。 application/octet-stream 默认值，可以下载所有类型
inputName：指定被下载文件的入口输入流, 和DownloadAction中的getInputStream()对应,主要是获得实际资源文件
contentDisposition：指定下载的文件名和显示方式,一般和文件名一致，但是要注意中文件名保存时乱码问题，解决办法就是进行编码处理
<!-- 指定由getTargetFile()方法返回被下载文件的InputStream -->
<param name="inputName">targetFile</param>
是下载的入口 我们不需要在我们的action里面配置targetFile变量 但需要getTargetFile方法，默认需要getInputStream()方法 也就是：inputName参数的值就是入口方法去掉get前缀、首字母小写的
字符串
我们的action里面的代码如下：
private String inputPath;//通过strtus获取文件地址 也可以直接写例如：String inputPath = ServletActionContext.getRequest().getRealPath("\uploads\document.pdf");
public void setInputPath(String value)
{
inputPath = value;
}
public InputStream getTargetFile() throws Exception
{
return ServletActionContext.getServletContext().getResourceAsStream(inputPath);
}
如果报以下错误：
Can not find a java.io.InputStream with the name [targetFile] in the invocation stack. Check the <param name="inputName"> tag specified for this action.
实际问题是ServletActionContext.getServletContext().getResourceAsStream(inputPath);找不到资源，请检查你的path是否正确。
而关于下载实际struts做了什么呢？我们看一部分源代码代码就很明白了：
HttpServletResponse oResponse = (HttpServletResponse) invocation.getInvocationContext().get(HTTP_RESPONSE);
// Set the content type
...
//Set the content length
...
// Set the content-disposition
...
// Set the cache control headers if neccessary
...
// Get the outputstream
//------------
oOutput = oResponse.getOutputStream();
if (LOG.isDebugEnabled()) {
LOG.debug("Streaming result [" + inputName + "] type=[" + contentType + "] length=[" + contentLength +
"] content-disposition=[" + contentDisposition + "] charset=[" + contentCharSet + "]");
}
// Copy input to output
LOG.debug("Streaming to output buffer +++ START +++");
byte[] oBuff = new byte[bufferSize];
int iSize;
while (-1 != (iSize = inputStream.read(oBuff))) {
oOutput.write(oBuff, 0, iSize);
}
LOG.debug("Streaming to output buffer +++ END +++");
// Flush
oOutput.flush();
}
finally {
if (inputStream != null) inputStream.close();
if (oOutput != null) oOutput.close();
}
//-----------
很简单，就像以前在servlet中一样通过getOutputStream 和配置content type ，content-disposition，cache control，content length这些参数的来实现。
这样就很简单的实现了下载功能。
以上是自己工作之余写的以下总结，不对的地方希望大家指点，谢谢，转载，请说明地址