如何用用Response下载文件（图片）

大致步骤：

• 获取下载文件路径
• 确定下载文件路径
• 设置浏览器支持的编码格式
• 获取下载文件的输入流
• 创建缓冲区
• 获取OutputStream对象
• 将FileInputStream流写入到buffer缓冲区中，使用OutputStream流将缓冲区的数据输出到客户端
• 配置web.xml

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public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取下载文件路径
        String realPath = "D:\\学习类\\Projects-java\\java-1-test\\JavaWebDemo\\src\\main\\resources\\111.png";
        System.out.println("下载文件路径：" + realPath);

        //确定下载文件路径
        String fileName = realPath.substring(realPath.lastIndexOf("//") + 1);

        //设置浏览器支持的编码格式
        resp.setHeader("Content-Disposition", "attachment;filename = " + URLEncoder.encode(fileName,"UTF-8"));

        //获取下载文件的输入流
        FileInputStream in = new FileInputStream(fileName);

        //创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];

        //获取OutputStream对象
        ServletOutputStream out = resp.getOutputStream();

        //将FileInputStream流写入到buffer缓冲区中，使用OutputStream流将缓冲区的数据输出到客户端
        while ((len = in.read(buffer)) > 0){
            out.write(buffer,0,len);
        }
        in.close();
        out.close();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}

---

配置web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
         xmlns="http://java.sun.com/xml/ns/j2ee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
    http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<servlet>
    <servlet-name>filedown</servlet-name>
    <servlet-class>com.xiaomu.FileServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>filedown</servlet-name>
    <url-pattern>/down</url-pattern>
</servlet-mapping>
</web-app>

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注意下载servlet-api和servlet-jsp

//web.xml的头
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
    http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
</web-app>


//javax.servlet-api
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.1.0</version>
    <scope>provided</scope>
</dependency>

//jsp
<dependency>
    <groupId>javax.servlet.jsp</groupId>
    <artifactId>javax.servlet.jsp-api</artifactId>
    <version>2.3.1</version>
    <scope>provided</scope>
</dependency>

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