如果调用okhttp工具类下载服务器文件报错

请按以下步骤检查：

1.动态申请权限，同时AndroidManifest.xml的application中添加

android:usesCleartextTraffic="true"

2.下载文件函数（downFile）在线程中调用

3.downFile的第二个参数文件路径写成相对路径（Environment.getExternalStorageDirectory() + "/download/"）

相关代码：

public void checkPemission() {
        Log.e("TAG", "进入了checkPemission()");
        int hasWritePermission = PermissionChecker.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE);
        if (hasWritePermission != PermissionChecker.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 9);
        } else {
            new Thread() {
                @Override
                public void run() {
                    super.run();
                    downFile(urlString);
                }
            }.start();
        }
    }

/**
 * 文件下载
 */
private void downFile(String url) {
    DownloadUtil.get().download(url, Environment.getExternalStorageDirectory() + "/pdf/", "test.pdf",
            new DownloadUtil.OnDownloadListener() {
                @Override
                public void onDownloadSuccess(File file) {

                    openPDF(file);//打开PDF文件
                }

                @Override
                public void onDownloading(int progress) {

                }

                @Override
                public void onDownloadFailed(Exception e) {
                    //下载异常进行相关提示操作

                }
            });
}

源码地址：  稍后附上

okhttp下载文件并直接显示到手机上