Java编程技巧：文件上传、下载、预览

1、上传文件

1.1、代码

@PostMapping("/uploadFile")
public String uploadFile(MultipartFile file) {
    System.out.println("文件名称：" + file.getOriginalFilename());
    return "成功";
}

@PostMapping("/uploadFile2")
public String uploadFile2(
        @RequestParam("file") MultipartFile file
) {
    System.out.println("文件名称：" + file.getOriginalFilename());
    return "成功";
}

@PostMapping("/uploadFile3")
public String uploadFile3(
        @RequestPart("file") MultipartFile file
) {
    System.out.println("文件名称：" + file.getOriginalFilename());
    return "成功";
}

// 发送文件的同时带上参数
@PostMapping("/uploadFile4")
public String uploadFile4(
        @RequestPart("file") MultipartFile file, // 可以换成“MultipartFile file”或者“@RequestParam("file") MultipartFile file”
        @RequestParam("id") String id
) {
    System.out.println("文件名称：" + file.getOriginalFilename());
    System.out.println("id：" + id);
    return "成功";
}

1.2、postman测试截图

2、下载resources目录中的模板文件

2.1、项目结构

假设resources目录下有一个pdf文件：用户数据导入模板.xlsx，然后我们来下载该文件

2.2、代码

import org.apache.tomcat.util.http.fileupload.IOUtils;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
import org.springframework.http.MediaType;
import org.springframework.http.MediaTypeFactory;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

@RestController
public class TestController {

	@GetMapping("/downloadLocalFile")
    public void downloadLocalFile(HttpServletResponse response) throws IOException {
        String fileName = "用户数据导入模板.xlsx";
        Resource r = new ClassPathResource(fileName);
        try (
                FileInputStream fileInputStream = new FileInputStream(r.getFile());
                ServletOutputStream outputStream = response.getOutputStream();
        ) {
            response.setContentType("application/force-download");
            try {
                fileName = new String(fileName.getBytes("utf-8"), "ISO-8859-1");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
            response.setHeader("Content-Disposition", "attachment;filename=" + fileName);
            IOUtils.copyLarge(fileInputStream, outputStream);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2.3、使用场景

3、预览文件

3.1、项目结构

以resources下面的文件为例，展示预览文件的代码，这是从本地获取文件，当然也可以通过其他方式获取文件

3.2、代码

import org.apache.tomcat.util.http.fileupload.IOUtils;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
import org.springframework.http.MediaType;
import org.springframework.http.MediaTypeFactory;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

@RestController
public class TestController {

	@GetMapping("/previewLocalFile")
    public void previewLocalFile(HttpServletResponse response) throws IOException {
        String fileName = "SQL必知必会（第5版）.pdf";
        Resource r = new ClassPathResource(fileName);
        try (
                FileInputStream fileInputStream = new FileInputStream(r.getFile());
                ServletOutputStream outputStream = response.getOutputStream();
        ) {
            // 区别点1：将“response.setContentType("application/force-download");”替换成下面内容
            response.setContentType(MediaTypeFactory.getMediaType(fileName).orElse(MediaType.APPLICATION_OCTET_STREAM).toString());
            try {
                fileName = new String(fileName.getBytes("utf-8"), "ISO-8859-1");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
            // 区别点2：预览是“filename”，下载是“attachment;filename=”
            response.setHeader("Content-Disposition", "filename=" + fileName);
            IOUtils.copyLarge(fileInputStream, outputStream);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

3.3、使用场景

在网盘软件中预览pdf文件