最近的程序都是部署在linux系统，原来需求是通过前端拼接地址，可以经过nginx的转发，请求到图片文件，但被客户提出这样不安全，需要加拦截判断，就改成文件由后台获取判断，符合了，就转成base64格式，返给前端。
有两种写法：
1：HTTP网络图片：

package com.xxxxx.xxxxx.xxxxx.controller;
import com.xxxxx.micro.common.util.ResultUtil;
import com.xxxxx.micro.common.web.BaseController;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiImplicitParam;
import io.swagger.annotations.ApiImplicitParams;
import io.swagger.annotations.ApiOperation;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.rmi.server.UID;
import java.util.Map;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang.StringUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import sun.misc.BASE64Encoder;

/**
 * @ClassName: pictureController
 * @Description:
 * @author: xxxxx
 * @create: 2021/12/3 14:28
 */
@RestController
@Api(tags = "接口改造-图片拦截")
@Slf4j
@RequestMapping("/weblogic")
public class PictureController extends BaseController {

    @GetMapping("/app/eomdoc/{url}")
    @ApiOperation(value = "查询图片,根据uid是否有效进行拦截", notes = "查询图片,根据uid是否有效进行拦截")
    @ApiImplicitParams({
            @ApiImplicitParam(name = "UID", value = "用户UID", required = true, paramType = "query"),
            @ApiImplicitParam(name = "type", value = "文件格式类型", required = true, paramType = "query"),
            @ApiImplicitParam(name="url", value="文件名称", required=true, paramType="query")
    })
    public String weblogic(@PathVariable String url,@RequestParam String type, String UID){

        Map<String, Object> params = this.getParams();

        if (StringUtils.isBlank(url) || StringUtils.isBlank(type) ){
            return this.responseJson(ResultUtil.error("参数缺失不完整"),null,null);
        }

        URL httUrl = null;
        InputStream is = null;
        ByteArrayOutputStream outStream = null;
        HttpURLConnection httpUrl = null;
        
        try {
            String path = "http://192.168.xxx.xx:xxxx/xxx/xxx/xxx/" + url + "." + type;
            //判断文件类型(jpg,jpeg,bmp,png,gif,tiff)
            log.info("******查询的文件类型是：" + type + "*********************");

            //判断文件类型，如果是图片类型--进行拦截，校验UID
            if(StringUtils.equalsIgnoreCase("jpg",type) || StringUtils.equalsIgnoreCase("jpeg",type) || StringUtils.equalsIgnoreCase("bmp",type) || StringUtils.equalsIgnoreCase("png",type) || StringUtils.equalsIgnoreCase("gif",type) || StringUtils.equalsIgnoreCase("tiff",type)){
                //参数-UID判空
                if (StringUtils.isBlank(UID)){
                    return this.responseJson(ResultUtil.error("参数UID缺失"),null,null);
                }
                //查询当前登录人
                Map<String, Object> loginUser = this.getLoginUser();
                if (loginUser == null){
                    return this.responseJson(ResultUtil.error("查询当前登录人失败"),null,null);
                }
            }

            httUrl = new URL(path);
            httpUrl = (HttpURLConnection) httUrl.openConnection();
            httpUrl.connect();
            httpUrl.getInputStream();
            is = httpUrl.getInputStream();
            outStream = new ByteArrayOutputStream();
            //每次读取的字符串长度，如果为-1，代表全部读取完毕
            int len = 0;
            //创建一个Buffer字符串
            byte[] buffer = new byte[1024];
            //使用一个输入流从buffer里把数据读取出来
            while( (len=is.read(buffer)) != -1 ){
                //用输出流往buffer里写入数据，中间参数代表从哪个位置开始读，len代表读取的长度
                outStream.write(buffer, 0, len);
            }
            // 对字节数组Base64编码
            System.out.print(new BASE64Encoder().encode(buffer));
            System.out.print(new BASE64Encoder().encode(outStream.toByteArray()));
            log.info("*****转base64:",new BASE64Encoder().encode(outStream.toByteArray()));
            String base64 = "data:image/jpg;base64,"+ new BASE64Encoder().encode(outStream.toByteArray());
            return base64;
        } catch (Exception e) {
            log.error("转base64失败",e);
            return "转base64失败";
        }

        //关闭，避免产生太多垃圾
        finally{
            if(is != null)
            {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(outStream != null)
            {
                try {
                    outStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(httpUrl != null)
            {
                httpUrl.disconnect();
            }
        }

    }

}