Servlet实现文件下载功能

本文实例为大家分享了servlet实现文件下载的具体代码，供大家参考，具体内容如下

把文件目录直接暴露给用户是很不安全的。所以要用servlet来做，而且这样做，文件的存储方式就更丰富了，可以是从文件系统上取来的，也可以是数据库中经过计算生成的，或者从其它什么稀奇古怪的地方取来的。

public class downloadservlet extends httpservlet {
  private string contenttype = "application/x-msdownload";
  private string enc = "utf-8";
  private string fileroot = "";


  /**
   * 初始化contenttype，enc，fileroot
   */
  public void init(servletconfig config) throws servletexception {
    string tempstr = config.getinitparameter("contenttype");
    if (tempstr != null && !tempstr.equals("")) {
      contenttype = tempstr;
    }
    tempstr = config.getinitparameter("enc");
    if (tempstr != null && !tempstr.equals("")) {
      enc = tempstr;
    }
    tempstr = config.getinitparameter("fileroot");
    if (tempstr != null && !tempstr.equals("")) {
      fileroot = tempstr;
    }
  }

  protected void doget(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {
    string filepath = request.getparameter("filepath");
    string fullfilepath = fileroot + filepath;
    /*读取文件*/
    file file = new file(fullfilepath);
    /*如果文件存在*/
    if (file.exists()) {
      string filename = urlencoder.encode(file.getname(), enc);
      response.reset();
      response.setcontenttype(contenttype);
      response.addheader("content-disposition", "attachment; filename=\"" + filename + "\"");
      int filelength = (int) file.length();
      response.setcontentlength(filelength);
      /*如果文件长度大于0*/
      if (filelength != 0) {
        /*创建输入流*/
        inputstream instream = new fileinputstream(file);
        byte[] buf = new byte[4096];
        /*创建输出流*/
        servletoutputstream servletos = response.getoutputstream();
        int readlength;
        while (((readlength = instream.read(buf)) != -1)) {
          servletos.write(buf, 0, readlength);
        }
        instream.close();
        servletos.flush();
        servletos.close();
      }
    }
  }

web.xml

  <servlet>
    <servlet-name>downloadservlet-name>
    <servlet-class>org.mstar.servlet.downloadservletservlet-class>
    <init-param>
      <param-name>filerootparam-name>
      <param-value>d:/tempparam-value>
    init-param>
    <init-param>
      <param-name>contenttypeparam-name>
      <param-value>application/x-msdownloadparam-value>
    init-param>
    <init-param>
      <param-name>encparam-name>
      <param-value>utf-8param-value>
    init-param>
  servlet>
  <servlet-mapping>
    <servlet-name>downloadservlet-name>
    <url-pattern>/downurl-pattern>
  servlet-mapping>

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。