Java读取第三方接口文件流返回前端预览、或保存文件（HttpURLConnection方式）_接口返回文件

package com.example.demo;
 
import cn.hutool.core.util.IdUtil;
import org.springframework.util.FileCopyUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
 
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
 
import static org.apache.catalina.manager.Constants.CHARSET;
 
@RestController
@RequestMapping("file")
public class TestController {
 
    /**
     * 前端下载文件
     * @param response
     * @throws UnsupportedEncodingException
     */
    @GetMapping(value = "/test1")
    public void test(HttpServletResponse response) throws UnsupportedEncodingException {
        // 设置编码
        response.setCharacterEncoding("UTF-8");
        response.setContentType("application/vnd.openxmlformats-officedocument.wordprocessingml.document");
        response.addHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode("test.pdf", "UTF-8"));
        String path = "D://test.pdf";
        try {
            FileInputStream in = new FileInputStream(new File(path));
            FileCopyUtils.copy(in, response.getOutputStream());
        } catch (FileNotFoundException e) {
            System.out.println("文件不存在");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
    /**
     * 前端预览文件
     * @param response
     * @throws IOException
     */
    @RequestMapping("download")
    public void download(HttpServletResponse response) throws IOException {
        String filePath = "D:\\test.pdf";
        System.out.println("filePath:" + filePath);
        File f = new File(filePath);
        if (!f.exists()) {
            response.sendError(404, "File not found!");
            return;
        }
        BufferedInputStream br = new BufferedInputStream(new FileInputStream(f));
        byte[] bs = new byte[1024];
        int len = 0;
        response.reset(); // 非常重要
        URL u = new URL("file:///" + filePath);
        String contentType = u.openConnection().getContentType();
        response.setContentType(contentType);
        response.setHeader("Content-Disposition", "inline;filename="
                + "test.pdf");
        // 文件名应该编码成utf-8，注意：使用时，我们可忽略这句
        OutputStream out = response.getOutputStream();
        while ((len = br.read(bs)) > 0) {
            out.write(bs, 0, len);
        }
        out.flush();
        out.close();
        br.close();
    }
 
    /**
     * 调用第三方流接口， 将文件保存到本地、读取本地文件返回前端预览
     * @param response
     * @throws IOException
     */
    @RequestMapping("test2")
    public void test2(HttpServletResponse response) throws IOException {
        HttpURLConnection urlConnection = null;
        FileOutputStream fileOutputStream;
        InputStream inputStream;
        String fileName = IdUtil.nanoId();
        try {
            URL url = new URL("http://localhost:8080/file/download");
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("POST");
            urlConnection.setConnectTimeout(20000);
            urlConnection.setDoOutput(true);
            urlConnection.setDoInput(true);
            urlConnection.setUseCaches(false);
            urlConnection.setRequestProperty("Content-Type", "application/json; charset=" + CHARSET);
            urlConnection.connect();
 
            File file = new File("D://"+fileName+".pdf");
            if (!file.getParentFile().exists()) {
                file.getParentFile().mkdirs();
            }
            if (!file.exists()) {
                file.createNewFile();
            }
            inputStream = urlConnection.getInputStream();
            BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);
            fileOutputStream = new FileOutputStream("D://"+fileName+".pdf");
            BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
 
            byte[] buf = new byte[4096];
            int length = bufferedInputStream.read(buf);
            while (-1 != length) {
                bufferedOutputStream.write(buf, 0, length);
                length = bufferedInputStream.read(buf);
            }
            bufferedInputStream.close();
            bufferedOutputStream.close();
        } catch (Exception e) {
            System.out.println("getFile error: " + e);
        } finally {
            if (null != urlConnection) {
                urlConnection.disconnect();
            }
        }
        String filePath = "D://"+fileName+".pdf";
        File f = new File("D://"+fileName+".pdf");
        if (!f.exists()) {
            response.sendError(404, "File not found!");
            return;
        }
        BufferedInputStream br = new BufferedInputStream(new FileInputStream(f));
        byte[] bs = new byte[1024];
        int len = 0;
        response.reset(); // 非常重要
        URL u = new URL("file:///" + filePath);
        String contentType = u.openConnection().getContentType();
        response.setContentType(contentType);
        response.setHeader("Content-Disposition", "inline;filename="
                + fileName + ".pdf");
        // 文件名应该编码成utf-8，注意：使用时，我们可忽略这句
        OutputStream out = response.getOutputStream();
        while ((len = br.read(bs)) > 0) {
            out.write(bs, 0, len);
        }
        out.flush();
        out.close();
        br.close();
    }
 
    /**
     * 调用第三方流接口， 将文件流返回前端预览
     * @param request
     * @param response
     */
    @RequestMapping("test3")
    public void test3(HttpServletRequest request, HttpServletResponse response) {
        HttpURLConnection urlConnection = null;
        InputStream inputStream;
        try {
            URL url = new URL("http://localhost:8080/file/download");
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("POST");
            urlConnection.setConnectTimeout(20000);
            urlConnection.setDoOutput(true);
            urlConnection.setDoInput(true);
            urlConnection.setUseCaches(false);
            urlConnection.setRequestProperty("Content-Type", "application/json; charset=" + CHARSET);
            urlConnection.connect();
            inputStream = urlConnection.getInputStream();
            BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);
            byte[] buf = new byte[4096];
            int length = bufferedInputStream.read(buf);
            ServletOutputStream out = response.getOutputStream();
            while (-1 != length) {
                out.write(buf, 0,length);
                length = bufferedInputStream.read(buf);
            }
            out.flush();
            out.close();
            bufferedInputStream.close();
        } catch (Exception e) {
            System.out.println("getFile error: " + e);
        } finally {
            if (null != urlConnection) {
                urlConnection.disconnect();
            }
        }
    }
}