转载:Struts2支持断点续传下载实现

转自：http://blog.sina.com.cn/s/blog_667ac0360102eckm.html

package com.ipan.core.controller.web.result;

import java.io.InputStream;
import java.io.OutputStream;
import java.net.SocketException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.catalina.connector.ClientAbortException;
import org.apache.commons.lang.StringUtils;
import org.apache.struts2.dispatcher.StreamResult;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.opensymphony.xwork2.ActionInvocation;

///
 // 支持断点续传文件输出流
 //
 // 对StreamResult做了增强，支持断点续传方式（多线程）下载同时也支持普通方式（单线程）下载；
 //
 // @author iPan
 // @version 2014-3-19
 //
public class MulitStreamResult extends StreamResult {

private static final long serialVersionUID = -256643510497634924L;
protected static Logger LOG = LoggerFactory.getLogger(MulitStreamResult.class);
@Override
protected void doExecute(String finalLocation, ActionInvocation invocation) throws Exception {
// Find the Response in context
HttpServletResponse response = (HttpServletResponse) invocation.getInvocationContext().get(HTTP_RESPONSE);
HttpServletRequest request = (HttpServletRequest) invocation.getInvocationContext().get(HTTP_REQUEST);
// Override any parameters using values on the stack
resolveParamsFromStack(invocation.getStack(), invocation);
String rangeStr = ""; // 范围字符串（比如“bytes=27000-”或者“bytes=27000-39000”的内容）
long fromLength = 0; // 起点长度（比如bytes=27000-39000，则这个值为27000）
long toLength = 0; // 终点长度（比如bytes=27000-39000，则这个值为39000）
long rangeLength = 0; // 响应的字节总量（toLength - fromLength + 1）
OutputStream out = null; // 输出流

if (inputStream == null) {
// Find the inputstream from the invocation variable stack
inputStream = (InputStream) invocation.getStack().findValue(conditionalParse(inputName, invocation));
}
if (inputStream == null) {
String msg = ("Can not find a java.io.InputStream with the name [" + inputName + "] in the invocation stack. " +
                   "Check the tag specified for this action.");
            LOG.error(msg);
            throw new IllegalArgumentException(msg);
}
if (contentLength == null || contentLength.length() < 1) {
throw new IllegalArgumentException("支持断点续传时，[Content-Length]不能为空.");
}
// Set the content type
if (contentCharSet != null && !contentCharSet.equals("")) {
response.setContentType(conditionalParse(contentType, invocation) + ";charset=" + contentCharSet);
} else {
response.setContentType(conditionalParse(contentType, invocation));
}

// Set the content-disposition
if (contentDisposition != null) {
response.addHeader("Content-Disposition", conditionalParse(contentDisposition, invocation));
}
// Set the cache control headers if neccessary
if (!allowCaching) {
response.addHeader("Pragma", "no-cache");
response.addHeader("Cache-Control", "no-cache");
}
// Set the content length
String _contentLength = conditionalParse(contentLength, invocation);
// 文件长度
int fileLength = Integer.parseInt(_contentLength);
response.setContentLength(fileLength);
// 需要使用断点续传下载
if (isHeadOfRange(request)) {
LOG.debug("断点续传下载.");
// 设置状态 HTTP/1.1 206 Partial Content
response.setStatus(javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT);
// 表示使用了断点续传（默认是“none”，可以不指定）
response.setHeader("Accept-Ranges", "bytes");
// 设置Content-Range
StringBuilder crBuf = new StringBuilder("bytes ");
rangeStr = request.getHeader("Range").replaceAll("bytes=", "").trim();
if (rangeStr.endsWith("-")) {
LOG.debug("开区间下载.");
rangeStr = StringUtils.substringBefore(rangeStr, "-");
fromLength = Long.parseLong(rangeStr);
rangeLength = fileLength - fromLength + 1;
crBuf.append(rangeStr).append("-").append(fromLength - 1).append("/").append(fileLength);
} else {
LOG.debug("闭区间下载.");
String num1 = StringUtils.substringBefore(rangeStr, "-");
String num2 = StringUtils.substringAfter(rangeStr, "-");
fromLength = Long.parseLong(num1);
toLength = Long.parseLong(num2);
rangeLength = toLength - fromLength + 1;
crBuf.append(rangeStr).append("/").append(fileLength);
}
// Content-Range: bytes [文件块的开始字节]-[文件的总大小 - 1]/[文件的总大小]
response.setHeader("Content-Range", crBuf.toString());
// 普通下载
} else {
LOG.debug("普通下载.");
// 默认返回 HTTP/1.1 200 OK
rangeLength = fileLength; // 客户端要求全文下载
}
// 输出文件操作
try {
out = response.getOutputStream();
byte[] outBuff = new byte[bufferSize];
int readLen = 0;
// 闭区间处理
if (toLength > 0) {
LOG.debug("闭区间下载开始...");
inputStream.skip(fromLength);
int readBufSize = (int) Math.min(bufferSize, rangeLength);
long pFrom = fromLength;
while (pFrom < toLength) {
readLen = inputStream.read(outBuff, 0, readBufSize);
pFrom += readBufSize;
readBufSize = (int) Math.min(readBufSize, toLength - pFrom + 1);
out.write(outBuff, 0, readLen);
}
// 开区间处理
} else {
LOG.debug("开区间下载开始...");
inputStream.skip(fromLength);
while ((readLen = inputStream.read(outBuff, 0, bufferSize)) != -1) {
out.write(outBuff, 0, readLen);
}
}
} catch (ClientAbortException e) {
// 忽略（迅雷等下载工具，支持多线程下载，但有些线程会被中途取消，导致异常。）
// LOG.debug(e.getMessage(), e);
} catch (SocketException e) {
// 忽略（迅雷等下载工具，支持多线程下载，但有些线程会被中途取消，导致异常。）
// LOG.debug(e.getMessage(), e);
} catch (Exception e) {
// 其他异常记录日志
LOG.error(e.getMessage(), e);
} finally {
if (inputStream != null) {
try {
inputStream.close();
} catch (Exception e) {
}
}
if (out != null) {
try {
out.flush();
} catch (Exception e1) {
}
try {
out.close();
} catch (Exception e) {
}
}
}
}

private static boolean isHeadOfRange(HttpServletRequest request) {
return request.getHeader("Range") != null;
}

}

个人补充：功能并未验证是否可行。