首先，解决两个小问题
1.输入中文乱码问题
一个小Demo即可解决：
package demo;import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class DemoServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { //设置response查询的码表
//response.setCharacterEncoding("UTF-8"); //通过一个头 Content-Type 告知客户端使用何种码表
//response.setHeader("Content-Type", "text/html;charset=UTF-8"); //以上两行可以简写成这样，Tomcat自动设置编码
response.setContentType("text/html;charset=UTF-8"); PrintWriter writer = response.getWriter();
//writer.write("hello response!!!");写英文不需要考虑编码问题
writer.write("你好"); } protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
2.怎么在客户端页面看到图片
用到字节流，示例如下：
package demo;import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class ByteServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { // 使用response获得字节输出流
ServletOutputStream out = response.getOutputStream(); // 获得服务器上的图片
String realPath = this.getServletContext().getRealPath("a.jpg");
InputStream in = new FileInputStream(realPath); // 字节数组提高效率
int len = 0;
byte[] buffer = new byte[1024];
while ((len = in.read(buffer)) > 0) {
out.write(buffer, 0, len);
} in.close();
out.close(); } protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
接下来是文件下载案例：
WebContent目录下创建download文件夹，放入各种文件，以供下载
这里有两种方式下载：
1.<a>标签直接指向服务器资源，浏览器显示能解析的，解析不了的提供下载
这种方式只需要html代码即可（新建download.html）
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>使用a标签指向服务器上的资源</h1>
<a href="/WEB4/download/a.flv" rel="external nofollow" rel="external nofollow" >a.flv</a>
<br />
<a href="/WEB4/download/a.jpg" rel="external nofollow" >a.jpg</a>
<br />
<a href="/WEB4/download/a.flv" rel="external nofollow" rel="external nofollow" >a.mp3</a>
<br />
<a href="/WEB4/download/a.mp4" rel="external nofollow" >a.mp4</a>
<br />
<a href="/WEB4/download/a.txt" rel="external nofollow" >a.txt</a>
<br />
<a href="/WEB4/download/a.zip" rel="external nofollow" >a.zip</a>
<br />
<h1>使用服务器端编码的方式实现文件下载</h1>
<a href="/WEB4/downloadServlet?filename=a.flv" rel="external nofollow" >a.flv</a>
<br />
<a href="/WEB4/downloadServlet?filename=a.jpg" rel="external nofollow" >a.jpg</a>
<br />
<a href="/WEB4/downloadServlet?filename=a.mp3" rel="external nofollow" >a.mp3</a>
<br />
<a href="/WEB4/downloadServlet?filename=a.mp4" rel="external nofollow" >a.mp4</a>
<br />
<a href="/WEB4/downloadServlet?filename=a.txt" rel="external nofollow" >a.txt</a>
<br />
<a href="/WEB4/downloadServlet?filename=a.zip" rel="external nofollow" >a.zip</a>
<br />
</body>
</html>
2.使用服务器端编码的方式实现文件下载
package demo;import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class DownloadServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 获得要下载文件名称
String filename = request.getParameter("filename");
// 下载的文件类型（MIME类型）
response.setContentType(this.getServletContext().getMimeType(filename));
// 告诉客户端该文件不是直接解析 而是以附件形式打开(下载)
response.setHeader("Content-Disposition", "attachment;filename=" + filename);
// 获取文件的绝对路径
String path = this.getServletContext().getRealPath("download/" + filename);
// 获得该文件输入流
InputStream in = new FileInputStream(path);
// 通过response获得输出流
ServletOutputStream out = response.getOutputStream();
// 文件拷贝
int len = 0;
byte[] buffer = new byte[1024];
while ((len = in.read(buffer)) > 0) {
out.write(buffer, 0, len);
}
in.close();
out.close();
} public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
还有一个小问题没有解决，文件名如果是中文，需要解决编码问题：
package demo;import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URLEncoder;import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import sun.misc.BASE64Encoder;public class DownloadServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { // *******文件名称是中文的下载******* // 获得要下载的文件的名称
String filename = request.getParameter("filename");
// 解决获得中文参数的乱码
filename = new String(filename.getBytes("ISO8859-1"), "UTF-8"); // 获得请求头中的User-Agent
String agent = request.getHeader("User-Agent");
// 根据不同浏览器进行不同的编码
String filenameEncoder = "";
if (agent.contains("MSIE")) {
// IE浏览器
filenameEncoder = URLEncoder.encode(filename, "utf-8");
filenameEncoder = filenameEncoder.replace("+", " ");
} else if (agent.contains("Firefox")) {
// 火狐浏览器
BASE64Encoder base64Encoder = new BASE64Encoder();
filenameEncoder = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
} else {
// 其它浏览器
filenameEncoder = URLEncoder.encode(filename, "utf-8");
} // 要下载的这个文件的类型-----客户端通过文件的MIME类型去区分类型
response.setContentType(this.getServletContext().getMimeType(filename));
// 告诉客户端该文件不是直接解析 而是以附件形式打开(下载)----filename="+filename 客户端默认对名字进行解码
response.setHeader("Content-Disposition", "attachment;filename=" + filenameEncoder); // 获取文件的绝对路径
String path = this.getServletContext().getRealPath("download/" + filename);
// 获得该文件的输入流
InputStream in = new FileInputStream(path);
// 获得输出流---通过response获得的输出流 用于向客户端写内容
ServletOutputStream out = response.getOutputStream();
// 文件拷贝的模板代码
int len = 0;
byte[] buffer = new byte[1024];
while ((len = in.read(buffer)) > 0) {
out.write(buffer, 0, len);
} in.close();
out.close(); } protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
注意事项：
1.response获得的流其实不需要手动关闭，Tomcat会自动关闭
2.response的getwrite和getoutputstream方法不能同时调用
