servlet学习总结（二）—图片下载和读取属性文件

2022-11-26 136

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简介： servlet学习总结（二）—图片下载和读取属性文件

引言

在上一篇博客中给大家介绍了一些servlet中的学习收获，在这篇博客中接着给大家分享servlet中图片的下载和属性文件的读取。

先看一下整个demo的目录结构;

1、图片的下载

package com.itheima.sc;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//实现中文文件的下载
public class ServletContextDemo6 extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    //文件在哪儿？以不变应万变
    ServletContext sc = getServletContext();
    String realPath = sc.getRealPath("/WEB-INF/classes/美女.jpg");//  文件存放的真实绝对路径
//    System.out.println(realPath);
    //构建文件的输入流
    InputStream in = new FileInputStream(realPath);
    //告知客户端以下载的方式打开：Content-Disposition=attachment;filename=27.jpg
    //获取要下载的文件名
    String filename  = realPath.substring(realPath.lastIndexOf(File.separator)+1);
    response.setHeader("Content-Type", "application/octet-stream");
    response.setHeader("Content-Disposition", "attachment;filename="+URLEncoder.encode(filename,"UTF-8"));//中文属于不安全的字符，需要进行URL编码
    //用response的字节流进行输出
    OutputStream out = response.getOutputStream();
    int len = -1;
    byte b[] = new byte[1024];
    while((len=in.read(b))!=-1){
      out.write(b, 0, len);
    }
    in.close();
    out.close();
  }
  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    doGet(request, response);
  }
}

上面的demo就是在browser中以下载的方式获取图片，仅仅是供学习和研究用，在实际的项目中一般是不会用这个原生的servlet来实现文件的下载和上传的。

2、servlet读取属性文件

在这给大家提供三种读取属性文件的方式，代码如下：

public class servletContextDemo07 extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    test10(request, response);
  }
  // 请不要把Tomcat等服务器装在有空格的目录中
  // 类加载器读取：只能读取classes或者类路径中的任意资源。但是不适合读取特别大的资源。b c
  private void test31(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    ClassLoader cl = servletContextDemo07.class.getClassLoader();// 得到类加载器
    URL url = cl.getResource("com/itheima/resources/c.properties");
    String path = url.getPath();
    InputStream in = new FileInputStream(path);
    Properties props = new Properties();
    props.load(in);
    System.out.println(props.getProperty("hello"));
  }
  // 类加载器读取：只能读取classes或者类路径中的任意资源。但是不适合读取特别大的资源。b c
  private void test30(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    ClassLoader cl = servletContextDemo07.class.getClassLoader();// 得到类加载器
    // InputStream in = cl.getResourceAsStream("b.properties");
    InputStream in = cl.getResourceAsStream("com/itheima/resources/c.properties");
    Properties props = new Properties();
    props.load(in);
    System.out.println(props.getProperty("hello"));
  }
  // 利用ResourceBundle读取：b c ，不能读a，只能读取properties的文件
  private void test20(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // ResourceBundle rb = ResourceBundle.getBundle("b");
    ResourceBundle rb = ResourceBundle.getBundle("com.itheima.resources.c");
    System.out.println(rb.getString("hello"));
  }
  // 利用ServletContext读取：a b c
  // 可以读取应用中任何位置上的资源。使用限制：只能在web应用中用
  private void test10(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // String path = getServletContext().getRealPath("/a.properties");
    // String path =
    // getServletContext().getRealPath("/WEB-INF/classes/b.properties");
    String path = getServletContext().getRealPath("/WEB-INF/classes/com/itheima/resources/c.properties");
    InputStream in = new FileInputStream(path);
    Properties props = new Properties();
    props.load(in);
    System.out.println(props.getProperty("hello"));
  }
  public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doGet(request, response);
  }
}