FileDownload.java：文件下载工具类
文件下载功能的工具类
JavaWeb工具类目录 [http://baike.xsoftlab.net/view/1059.html](http://baike.xsoftlab.net/view/1059.html)
基础版本：
```java
package com.zhenzhigu.commons.util;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 下载文件 创建人：Master.Xia 创建时间：2014年06月08日
*
* @version
*/
public class FileDownload {
/**
* @param request
* @param response
* @param fileAbsPath 文件绝对路径(包括文件名和扩展名)
* @param showName 下载后看到的文件名
* @return 文件名
*/
public static void execute(HttpServletRequest request,HttpServletResponse response, InputStream input,long length, String showName)throws Exception {
String info = request.getHeader("User-Agent").toLowerCase();
if (info.contains("firefox")) { // Firefox
showName = new String(showName.getBytes(), "ISO-8859-1");
} else { // IE,Chrome
showName = URLEncoder.encode(showName, "UTF-8");
}
response.reset(); // 响应重置
response.setHeader("Content-Disposition", "attachment; filename=\""+ showName + "\"");
response.addHeader("Content-Length", ""+length);
response.setContentType("application/octet-stream;charset=UTF-8");
OutputStream out = response.getOutputStream();
int len = 0;
byte[] buffer = new byte[1024*8];
while ((len = input.read(buffer)) != -1) {
out.write(buffer,0,len);
}
input.close();
response.flushBuffer();
}
public static void execute(HttpServletRequest request,
HttpServletResponse response, File file, String showName)
throws Exception {
execute(request, response, new FileInputStream(file), file.length(), showName);
}
public static void execute(HttpServletRequest request, HttpServletResponse response, String fileAbsPath, String showName) throws Exception{
execute(request, response, new File(fileAbsPath), showName);
}
}
```
支持断点续传的升级版本：
```java
package com.itshidu.commons.web.utils;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 下载文件
* @author Master.Xia
* @version 1.0 (2014.07.16)
* @version 1.1 (2018.02.16)
* @version 1.2 (2018.09.30)
*/
public class FileDownload {
/**
* 请求转发到一个指定的文件，就像浏览器直接访问这个文件一样，不会弹框提示
* @param request (请求)
* @param response (响应)
* @param file (访问的文件)
* @throws Exception (异常)
*/
public static void forward(HttpServletRequest request,HttpServletResponse response,File file)throws Exception {
forward(request, response, file, null, false);
}
/**
* 请求转发到一个指定的文件，就像浏览器直接访问这个文件一样，如果遇到浏览器不认识的文件类型，则会下载它，支持断点续传。
* 当isAttachment为true时会有下载提示框
* @param request (请求)
* @param response (响应)
* @param file (访问的文件)
* @param name (下载时在浏览器显示的名字)
* @param isAttachment (浏览器是否弹出下载框，true弹框，false不弹框)
* @throws Exception (异常)
*/
public static void forward(HttpServletRequest request,HttpServletResponse response,File file,String name,boolean isAttachment)throws Exception {
Path path = Paths.get(file.getAbsolutePath());
int length = (int)file.length();
int start = 0;
int end = length - 1;
String range = request.getHeader("Range");
if(range!=null&&range.length()>0) {
range = range.toLowerCase(); //RANGE:BYTES=100-500
range = range.replaceAll("\\s*", ""); //去除字符串中所有的不可见字符
if(range.contains("bytes=")) {//bytes=100
if(range.contains("-")) {
String a = range.substring(6, range.indexOf("-"));
start = Integer.parseInt(a);
if(range.charAt(range.length()-1)!='-') {
String b = range.substring(range.indexOf("-")+1);
end = Integer.parseInt(b);
}
}else {
String a = range.substring(6);
start = Integer.parseInt(a);
}
}
}
int contentLength = end - start + 1;
response.reset();
response.setHeader("Accept-Ranges", "bytes");
response.setContentType(Files.probeContentType(path));
response.setHeader("Content-Range",String.format("bytes %s-%s/%s", start, end, length));
response.setHeader("Content-Length", String.format("%s", contentLength));
response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
if(isAttachment) {
//如果是下载，则弹框提示，解决乱码问题
String info = request.getHeader("User-Agent").toLowerCase();
String showName = file.getName();
if(name!=null&&name.length()>0)showName=name;
if (info.contains("firefox")) { // Firefox
showName = new String(showName.getBytes(), "ISO-8859-1");
} else { // IE,Chrome
showName = URLEncoder.encode(showName, "UTF-8");
}
response.setHeader("Content-Disposition", "attachment; filename=\""+ showName + "\"");
}
//数据传输
InputStream in = null;
try{
in = new FileInputStream(file);
int len,remain = contentLength;
byte[] buffer = new byte[1024*8];
OutputStream out = response.getOutputStream();
int plan = start;
while(plan>0){
plan -= in.skip(plan);
}
while((len=in.read(buffer))!=-1 && remain > 0) {
out.write(buffer, 0, (remain<len? remain:len) );
}
}catch (Exception e) {
throw e;
}finally {
try {in.close(); } catch (Exception e2) { }
}
}
}
```