打开文件选择器

// 打开系统的文件选择器
public void pickFile(View view) {
    Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
    intent.addCategory(Intent.CATEGORY_OPENABLE);
    intent.setType("*/*");
    this.startActivityForResult(intent, REQUEST_CODE);
}

获取文件的真实路径

// 获取文件的真实路径
@Override
protected void onActivityResult(final int requestCode, final int resultCode, @Nullable final Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (data == null) {
        // 用户未选择任何文件，直接返回
        return;
    }
    Uri uri = data.getData(); // 获取用户选择文件的URI
    // 通过ContentProvider查询文件路径
    ContentResolver resolver = this.getContentResolver();
    Cursor cursor = resolver.query(uri, null, null, null, null);
    if (cursor == null) {
        // 未查询到，说明为普通文件，可直接通过URI获取文件路径
        String path = uri.getPath();
        return;
    }
    if (cursor.moveToFirst()) {
        // 多媒体文件，从数据库中获取文件的真实路径
        String path = cursor.getString(cursor.getColumnIndex("_data"));
    }
    cursor.close();
}

使用OkHttp上传文件

// 使用OkHttp上传文件
public void uploadFile(File file) {
    OkHttpClient client = new OkHttpClient();
    MediaType contentType = MediaType.parse("text/plain"); // 上传文件的Content-Type
    RequestBody body = RequestBody.create(contentType, file); // 上传文件的请求体
    Request request = new Request.Builder()
            .url("https://api.github.com/markdown/raw") // 上传地址
            .post(body)
            .build();
    Call call = client.newCall(request);
    call.enqueue(new Callback() {
        @Override
        public void onResponse(Call call, Response response) throws IOException {
            // 文件上传成功
            if (response.isSuccessful()) {
                Log.i("Haoxueren", "onResponse: " + response.body().string());
            } else {
                Log.i("Haoxueren", "onResponse: " + response.message());
            }
        }

        @Override
        public void onFailure(Call call, IOException e) {
            // 文件上传失败
            Log.i("Haoxueren", "onFailure: " + e.getMessage());
        }
    });
}