Javaプレビューpdfファイル

package com.ctdcn.business.pdfInfo.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;

import javax.servlet.http.HttpServletResponse;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

@Controller
public class demo {

    @GetMapping("showpdf")
    public String showpdf(HttpServletResponse response) throws IOException {
        //    
        InputStream in = new FileInputStream("C:\\ctdFile\
ewPdf\\ab784ec2-6c25-4186-9351-18ad5e61d9be-NZ-CNS-9.pdf");
        byte[] data = toByteArray(in);
        if(data.length == 0 && data == null){
            return "    ";
        }
        //   
        response.setContentType("application/pdf");
        OutputStream out = response.getOutputStream();
        out.write(data);
        return "ok";
    }

    /**
     *      
     * @param in
     * @return
     * @throws IOException
     */
    private byte[] toByteArray(InputStream in) throws IOException {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024 * 4];
        int n = 0;
        while ((n = in.read(buffer)) != -1) {
            out.write(buffer, 0, n);
        }
        byte[] bytes = out.toByteArray();
        return bytes;
    }
}