java调用手机摄像头

要在Java中调用手机摄像头，需要使用Android SDK提供的相机API。以下是一个简单的示例代码，可以启动相机并显示预览：

import android.app.Activity;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.os.Bundle;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.Button;

public class CameraActivity extends Activity implements SurfaceHolder.Callback {
    private Camera camera;
    private SurfaceView surfaceView;
    private SurfaceHolder surfaceHolder;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera);

        surfaceView = (SurfaceView) findViewById(R.id.surfaceView);
        surfaceHolder = surfaceView.getHolder();
        surfaceHolder.addCallback(this);
        surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);

        Button captureButton = (Button) findViewById(R.id.captureButton);
        captureButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (camera != null) {
                    camera.takePicture(null, null, pictureCallback);
                }
            }
        });
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        try {
            camera = Camera.open();
            camera.setPreviewDisplay(holder);
            camera.startPreview();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        if (camera != null) {
            camera.stopPreview();
            try {
                camera.setPreviewDisplay(holder);
                camera.startPreview();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        if (camera != null) {
            camera.stopPreview();
            camera.release();
            camera = null;
        }
    }

    private Camera.PictureCallback pictureCallback = new Camera.PictureCallback() {
        @Override
        public void onPictureTaken(byte[] data, Camera camera) {
            // 处理拍摄的照片数据
        }
    };
}

要调用此Activity，需要在应用程序的AndroidManifest.xml文件中添加以下权限：

<uses-permission android:name="android.permission.CAMERA" />

并在应用程序的build.gradle文件中添加以下依赖项：

dependencies {
    implementation 'com.android.support:support-v4:28.0.0'
}