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">a.flv</a> <br /> <a href="/WEB4/download/a.jpg">a.jpg</a> <br /> <a href="/WEB4/download/a.flv">a.mp3</a> <br /> <a href="/WEB4/download/a.mp4">a.mp4</a> <br /> <a href="/WEB4/download/a.txt">a.txt</a> <br /> <a href="/WEB4/download/a.zip">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">a.flv</a> <br /> <a href="/WEB4/downloadServlet?filename=a.jpg">a.jpg</a> <br /> <a href="/WEB4/downloadServlet?filename=a.mp3">a.mp3</a> <br /> <a href="/WEB4/downloadServlet?filename=a.mp4">a.mp4</a> <br /> <a href="/WEB4/downloadServlet?filename=a.txt">a.txt</a> <br /> <a href="/WEB4/downloadServlet?filename=a.zip">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