SpringMvc高级（拦截器和文件上传下载）

拦截器（Interceptor）是一种常用的设计模式，在软件工程领域被广泛应用。拦截器通常被用来处理各种请求和响应，可以在请求发送前或响应返回后进行一系列的操作和处理。拦截器可以用于请求身份认证、日志记录、性能优化、权限控制、数据加密等等，是很多框架和中间件中常用的一种组件。

在Java中，拦截器一般是通过实现javax.servlet.Filter接口或Spring框架中的HandlerInterceptor接口来实现的。拦截器可以被用于Web应用程序、消息队列、RPC调用等各种情况。

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
 
public class MyInterceptor implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // 初始化操作，可以为空
    }
 
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        HttpServletResponse httpResponse = (HttpServletResponse) response;
 
        // 在此处可以进行各种拦截操作，例如身份认证、权限控制、日志记录等等
        // 这里只是一个简单的示例：在请求头中添加一个自定义的字段
        httpResponse.setHeader("My-Interceptor", "Hello World!");
 
        chain.doFilter(request, response);
    }
 
    @Override
    public void destroy() {
        // 销毁操作，可以为空
    }
}
 

<filter>
    <filter-name>MyInterceptorfilter-name>
    <filter-class>com.example.MyInterceptorfilter-class>
filter>
 
<filter-mapping>
    <filter-name>MyInterceptorfilter-name>
    <url-pattern>*url-pattern>
filter-mapping>
 

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
 
public class MyServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String header = req.getHeader("My-Interceptor");
        resp.getWriter().write(header != null ? header : "Header Not Set");
    }
 
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}
 

文件上下载

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
 
public class FileUploader {
    private static final String UPLOAD_URL = "http://example.com/upload"; // 上传文件的URL地址
    private static final String FILE_PATH = "path/to/file"; // 要上传的文件路径
 
    public static void main(String[] args) throws IOException {
        File file = new File(FILE_PATH);
        if (!file.exists()) {
            System.out.println("文件不存在");
            return;
        }
 
        URL url = new URL(UPLOAD_URL);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
 
        conn.setRequestMethod("POST");
        conn.setDoOutput(true);
        conn.setRequestProperty("Content-Type", "application/octet-stream"); // 文件类型
        conn.setRequestProperty("filename", file.getName()); // 文件名
 
        InputStream in = new FileInputStream(file);
        byte[] buffer = new byte[1024];
        int len;
        while ((len = in.read(buffer)) != -1) {
            conn.getOutputStream().write(buffer, 0, len);
        }
        in.close();
 
        if (conn.getResponseCode() == HttpURLConnection.HTTP_OK) {
            System.out.println("上传成功");
        } else {
            System.out.println("上传失败");
        }
        conn.disconnect();
    }
}
 

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
 
public class FileDownloader {
    private static final String DOWNLOAD_URL = "http://example.com/download"; // 下载文件的URL地址
    private static final String FILE_PATH = "path/to/save/file"; // 要保存的文件路径
 
    public static void main(String[] args) throws IOException {
        URL url = new URL(DOWNLOAD_URL);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
 
        conn.setRequestMethod("GET");
        conn.setDoOutput(true);
 
        InputStream in = conn.getInputStream();
        FileOutputStream out = new FileOutputStream(FILE_PATH);
        byte[] buffer = new byte[1024];
        int len;
        while ((len = in.read(buffer)) != -1) {
            out.write(buffer, 0, len);
        }
        in.close();
        out.close();
 
        if (conn.getResponseCode() == HttpURLConnection.HTTP_OK) {
            System.out.println("下载成功");
        } else {
            System.out.println("下载失败");
        }
        conn.disconnect();
    }
}