Hey there! Since you're only 5 days into learning Java and Android Studio, let's break this down step by step—no confusing jargon, just actionable steps to fix your issue.

1. 先搞定基础权限（最容易忽略的根源） #

Android需要明确权限才能访问相机和存储，很多“找不到文件”的问题都出在这：

• 在AndroidManifest.xml里添加静态权限：

<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" android:maxSdkVersion="28" />
<uses-feature android:name="android.hardware.camera" android:required="true" />

<!-- Android 7+ 必须用FileProvider避免文件暴露问题 -->
<application ...>
    <provider
        android:name="androidx.core.content.FileProvider"
        android:authorities="${applicationId}.fileprovider"
        android:exported="false"
        android:grantUriPermissions="true">
        <meta-data
            android:name="android.support.FILE_PROVIDER_PATHS"
            android:resource="@xml/file_paths" />
    </provider>
</application>

• 创建res/xml/file_paths.xml文件，指定相机照片的合法存储路径：

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-files-path name="my_images" path="Pictures" />
</paths>

• 动态申请权限（Android 6.0+强制要求）：在MainActivity里添加逻辑，确保用户允许相机权限后再打开相机。

2. 正确创建拍照文件并指定路径 #

全分辨率照片不能靠Intent返回的data获取（那只是缩略图），必须提前创建一个文件，让相机直接保存到这个文件里：

// 在MainActivity里定义全局变量
private File photoFile;
private Uri photoUri;

// 生成唯一拍照文件的方法
private File createImageFile() throws IOException {
    String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss", Locale.getDefault()).format(new Date());
    String imageFileName = "JPEG_" + timeStamp + "_";
    // 用App私有外部目录，避免权限冲突
    File storageDir = getExternalFilesDir(Environment.DIRECTORY_PICTURES);
    return File.createTempFile(imageFileName, ".jpg", storageDir);
}

3. 打开相机的正确姿势（适配新版API） #

用registerForActivityResult替代已弃用的onActivityResult，更简洁安全：

// 初始化相机回调
ActivityResultLauncher<Intent> cameraLauncher = registerForActivityResult(
    new ActivityResultContracts.StartActivityForResult(),
    result -> {
        if (result.getResultCode() == RESULT_OK) {
            // 拍照成功后，photoFile就是全分辨率照片的文件
            if (photoFile.exists()) {
                // 显示照片到ImageView
                loadFullSizeImage(photoFile, yourImageView);
                // 调用上传方法
                uploadPhotoToServer(photoFile);
            } else {
                Toast.makeText(this, "Photo not found!", Toast.LENGTH_SHORT).show();
            }
        }
    }
);

// ImageView的点击事件
yourImageView.setOnClickListener(v -> {
    // 先检查相机权限
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
        ActivityResultLauncher<String[]> permissionLauncher = registerForActivityResult(
            new ActivityResultContracts.RequestMultiplePermissions(),
            permissions -> {
                Boolean cameraGranted = permissions.getOrDefault(Manifest.permission.CAMERA, false);
                if (cameraGranted) openCamera();
                else Toast.makeText(this, "需要相机权限才能拍照", Toast.LENGTH_SHORT).show();
            }
        );
        permissionLauncher.launch(new String[]{Manifest.permission.CAMERA});
    } else {
        openCamera();
    }
});

// 打开相机的具体逻辑
private void openCamera() {
    Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
    if (takePictureIntent.resolveActivity(getPackageManager()) != null) {
        try {
            photoFile = createImageFile();
            if (photoFile != null) {
                // 用FileProvider生成合法Uri
                photoUri = FileProvider.getUriForFile(this,
                    getPackageName() + ".fileprovider",
                    photoFile);
                takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, photoUri);
                cameraLauncher.launch(takePictureIntent);
            }
        } catch (IOException ex) {
            Toast.makeText(this, "创建照片文件失败：" + ex.getMessage(), Toast.LENGTH_SHORT).show();
        }
    }
}

4. 加载全分辨率照片到ImageView（避免内存溢出） #

直接加载大图片会导致OOM，要先缩放再显示：

private void loadFullSizeImage(File imageFile, ImageView imageView) {
    BitmapFactory.Options options = new BitmapFactory.Options();
    // 先只获取图片尺寸，不加载到内存
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeFile(imageFile.getAbsolutePath(), options);
    // 计算缩放比例，适配ImageView大小
    int reqWidth = imageView.getWidth();
    int reqHeight = imageView.getHeight();
    int inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
    // 加载缩放后的图片
    options.inJustDecodeBounds = false;
    options.inSampleSize = inSampleSize;
    Bitmap bitmap = BitmapFactory.decodeFile(imageFile.getAbsolutePath(), options);
    imageView.setImageBitmap(bitmap);
}

private int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
    final int height = options.outHeight;
    final int width = options.outWidth;
    int inSampleSize = 1;
    if (height > reqHeight || width > reqWidth) {
        final int halfHeight = height / 2;
        final int halfWidth = width / 2;
        while ((halfHeight / inSampleSize) >= reqHeight
               && (halfWidth / inSampleSize) >= reqWidth) {
            inSampleSize *= 2;
        }
    }
    return inSampleSize;
}

5. 排查“photo not found”的常见原因 #

• 文件创建失败：检查createImageFile里的存储目录是否存在，有没有写入权限。
• Uri配置错误：确保FileProvider的authorities和代码里的一致，file_paths.xml路径正确。
• 权限未通过：用户拒绝了相机权限，导致相机无法保存照片。
• 版本适配问题：Android 10+用分区存储，不能直接访问公共目录，要用App私有目录（代码里的getExternalFilesDir）。

6. 上传照片到网站的基本思路 #

用OkHttp（比原生API简单）实现文件上传：

private void uploadPhotoToServer(File photoFile) {
    OkHttpClient client = new OkHttpClient();
    RequestBody requestBody = new MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart("photo", photoFile.getName(),
            RequestBody.create(MediaType.parse("image/jpeg"), photoFile))
        .build();
    Request request = new Request.Builder()
        .url("你的网站上传接口地址")
        .post(requestBody)
        .build();
    client.newCall(request).enqueue(new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {
            runOnUiThread(() -> Toast.makeText(MainActivity.this, "上传失败：" + e.getMessage(), Toast.LENGTH_SHORT).show());
        }
        @Override
        public void onResponse(Call call, Response response) throws IOException {
            if (response.isSuccessful()) {
                runOnUiThread(() -> Toast.makeText(MainActivity.this, "上传成功！", Toast.LENGTH_SHORT).show());
            } else {
                runOnUiThread(() -> Toast.makeText(MainActivity.this, "上传失败：服务器返回错误", Toast.LENGTH_SHORT).show());
            }
        }
    });
}

记得在build.gradle里添加OkHttp依赖：

dependencies {
    implementation 'com.squareup.okhttp3:okhttp:4.10.0'
}

内容的提问来源于stack exchange，提问作者Michael Burns