需求： 在工程中，放置WORD模板檔案供使用者下載

功能：頁面提供下載連結，使用者點選連結後，實現檔案下載。

理解：剛開始以為直接用超連結指向檔案即可，或用js實現，後來發現都不行。

實現：最後在網上搜了一個實現HTTP檔案下載的java類，只要呼叫如下程式碼即可。

下面程式碼放在request經過的地方都可以，如servlet,struts的action或jsp頁面。

basePath =  "啊啊啊.doc"; // 我用的是servlet，啊啊啊.doc放在root根目錄下
DownLoadUtil su = new DownLoadUtil();
su.initialize(request.getSession().getServletContext(), request,
response);
su.setContentDisposition(null);
su.downloadFile(basePath);

以下為java下載類程式碼：

package com.test;


import java.io.FileInputStream;
import java.io.IOException;


import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;


public class DownLoadUtil {


protected ServletContext m_application;
private boolean m_denyPhysicalPath;
protected HttpServletResponse m_response;
private String m_contentDisposition;
protected HttpServletRequest m_request;


public final void initialize(ServletConfig servletconfig,
HttpServletRequest httpservletrequest,
HttpServletResponse httpservletresponse) throws ServletException {
m_application = servletconfig.getServletContext();
m_request = httpservletrequest;
m_response = httpservletresponse;
}


public final void initialize(ServletContext context,HttpServletRequest request,HttpServletResponse response)
throws ServletException {
m_application = context;
m_request = (HttpServletRequest) request;
m_response = (HttpServletResponse) response;
}


public final void initialize(ServletContext servletcontext,
HttpSession httpsession, HttpServletRequest httpservletrequest,
HttpServletResponse httpservletresponse, JspWriter jspwriter)
throws ServletException {
m_application = servletcontext;
m_request = httpservletrequest;
m_response = httpservletresponse;
}


public void setContentDisposition(String s) {
m_contentDisposition = s;
}


public void downloadFile(String s) throws IOException {
downloadFile(s, null, null);
}


public void downloadFile(String s, String s1) throws IOException {
downloadFile(s, s1, null);
}


public void downloadFile(String s, String s1, String s2) throws IOException {
downloadFile(s, s1, s2, 65000);
}


public void downloadFile(String s, String s1, String s2, int i)
throws IOException {
if (s == null) {
throw new IllegalArgumentException("File '" + s
+ "' not found (1040).");
}
if (s.equals(""))
throw new IllegalArgumentException("File '" + s
+ "' not found (1040).");
if (!isVirtual(s) && m_denyPhysicalPath)
throw new SecurityException("Physical path is denied (1035).");
if (isVirtual(s))
s = m_application.getRealPath(s);
java.io.File file = new java.io.File(s);
FileInputStream fileinputstream = new FileInputStream(file);
long l = file.length();
int k = 0;
byte abyte0[] = new byte[i];
if (s1 == null)
m_response.setContentType("application/x-msdownload");
else if (s1.length() == 0)
m_response.setContentType("application/x-msdownload");
else
m_response.setContentType(s1);
m_response.setContentLength((int) l);
m_contentDisposition = m_contentDisposition != null ? m_contentDisposition
: "attachment;";
if (s2 == null)
m_response.setHeader("Content-Disposition", m_contentDisposition
+ " filename=" + toUtf8String(getFileName(s)));
else if (s2.length() == 0)
m_response.setHeader("Content-Disposition", m_contentDisposition);
else
m_response.setHeader("Content-Disposition", m_contentDisposition
+ " filename=" + toUtf8String(s2));
while ((long) k < l) {
int j = fileinputstream.read(abyte0, 0, i);
k += j;
m_response.getOutputStream().write(abyte0, 0, j);
}
fileinputstream.close();
}


private boolean isVirtual(String s) {
if (m_application.getRealPath(s) != null) {
java.io.File file = new java.io.File(m_application.getRealPath(s));
return file.exists();
} else {
return false;
}
}


private String getFileName(String s) {
int i = 0;
i = s.lastIndexOf(47);
if (i != -1)
return s.substring(i + 1, s.length());
i = s.lastIndexOf(92);
if (i != -1)
return s.substring(i + 1, s.length());
else
return s;
}


public static String toUtf8String(String s) {
StringBuffer sb = new StringBuffer();
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (c >= 0 && c <= 255) {
sb.append(c);
} else {
byte[] b;
try {
b = Character.toString(c).getBytes("utf-8");
} catch (Exception ex) {
b = new byte[0];
}
for (int j = 0; j < b.length; j++) {
int k = b[j];
if (k < 0)
k += 256;
sb.append("%" + Integer.toHexString(k).toUpperCase());
}
}
}
return sb.toString();
}


}