1. Manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.camera2te"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="21"
        android:targetSdkVersion="21" />
    <uses-permission android:name="android.permission.CAMERA" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-feature android:name="android.hardware.camera2.full" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

2. layout

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.camera2te.MainActivity" >

    <TextureView
        android:id="@+id/texture"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true" />
   
    <Button
        android:id="@+id/btn_takepicture"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="@string/picture" />

</RelativeLayout>

3. Java file

package com.example.camera2te;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import android.app.Activity;
import android.content.Context;
import android.media.Image;
import android.media.ImageReader;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.HandlerThread;
import android.util.Log;
import android.util.Size;
import android.util.SparseIntArray;
import android.view.Surface;
import android.view.TextureView;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.Toast;
import android.graphics.ImageFormat;
import android.graphics.SurfaceTexture;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraCaptureSession;
import android.hardware.camera2.CameraCharacteristics;
import android.hardware.camera2.CameraDevice;
import android.hardware.camera2.CameraManager;
import android.hardware.camera2.CameraMetadata;
import android.hardware.camera2.CaptureRequest;
import android.hardware.camera2.TotalCaptureResult;
import android.hardware.camera2.params.StreamConfigurationMap;

public class MainActivity extends Activity {
	
	private final static String TAG = "Camera2testJ";
	private Size mPreviewSize;
	
	private TextureView mTextureView;
	private CameraDevice mCameraDevice;
	private CaptureRequest.Builder mPreviewBuilder;
	private CameraCaptureSession mPreviewSession;
	
	private Button mBtnShot;
	
	private static final SparseIntArray ORIENTATIONS = new SparseIntArray();

    static {
        ORIENTATIONS.append(Surface.ROTATION_0, 90);
        ORIENTATIONS.append(Surface.ROTATION_90, 0);
        ORIENTATIONS.append(Surface.ROTATION_180, 270);
        ORIENTATIONS.append(Surface.ROTATION_270, 180);
    }
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		requestWindowFeature(Window.FEATURE_NO_TITLE);
		getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
		setContentView(R.layout.activity_main);
		
		mTextureView = (TextureView)findViewById(R.id.texture);
		mTextureView.setSurfaceTextureListener(mSurfaceTextureListener);
		
		mBtnShot = (Button)findViewById(R.id.btn_takepicture);
		mBtnShot.setOnClickListener(new OnClickListener(){

			@Override
			public void onClick(View v) {
				Log.e(TAG, "mBtnShot clicked");
				takePicture();
			}
			
		});

	}

	protected void takePicture() {
		Log.e(TAG, "takePicture");
		if(null == mCameraDevice) {
			Log.e(TAG, "mCameraDevice is null, return");
			return;
		}
		
		CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
		try {
			CameraCharacteristics characteristics = manager.getCameraCharacteristics(mCameraDevice.getId());
			
			Size[] jpegSizes = null;
			if (characteristics != null) {
	            jpegSizes = characteristics
	                    .get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP)
	                    .getOutputSizes(ImageFormat.JPEG);
	        }
			int width = 640;
            int height = 480;
            if (jpegSizes != null && 0 < jpegSizes.length) {
                width = jpegSizes[0].getWidth();
                height = jpegSizes[0].getHeight();
            }
            
            ImageReader reader = ImageReader.newInstance(width, height, ImageFormat.JPEG, 1);
            List<Surface> outputSurfaces = new ArrayList<Surface>(2);
            outputSurfaces.add(reader.getSurface());
            outputSurfaces.add(new Surface(mTextureView.getSurfaceTexture()));
            
            final CaptureRequest.Builder captureBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
            captureBuilder.addTarget(reader.getSurface());
            captureBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
            
            // Orientation
            int rotation = getWindowManager().getDefaultDisplay().getRotation();
            captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));

            final File file = new File(Environment.getExternalStorageDirectory()+"/DCIM", "pic.jpg");

            ImageReader.OnImageAvailableListener readerListener = new ImageReader.OnImageAvailableListener() {

				@Override
				public void onImageAvailable(ImageReader reader) {

					Image image = null;
					try {
                        image = reader.acquireLatestImage();
                        ByteBuffer buffer = image.getPlanes()[0].getBuffer();
                        byte[] bytes = new byte[buffer.capacity()];
                        buffer.get(bytes);
                        save(bytes);
                    } catch (FileNotFoundException e) {
                        e.printStackTrace();
                    } catch (IOException e) {
                        e.printStackTrace();
                    } finally {
                        if (image != null) {
                            image.close();
                        }
                    }
				}

				private void save(byte[] bytes) throws IOException {
                    OutputStream output = null;
                    try {
                        output = new FileOutputStream(file);
                        output.write(bytes);
                    } finally {
                        if (null != output) {
                            output.close();
                        }
                    }
                }
            	
            };
            
            HandlerThread thread = new HandlerThread("CameraPicture");
            thread.start();
            final Handler backgroudHandler = new Handler(thread.getLooper());
            reader.setOnImageAvailableListener(readerListener, backgroudHandler);
            
            final CameraCaptureSession.CaptureCallback captureListener = new CameraCaptureSession.CaptureCallback() {

				@Override
				public void onCaptureCompleted(CameraCaptureSession session,
						CaptureRequest request, TotalCaptureResult result) {

					super.onCaptureCompleted(session, request, result);
					Toast.makeText(MainActivity.this, "Saved:"+file, Toast.LENGTH_SHORT).show();
					startPreview();
				}
            	
            };
            
            mCameraDevice.createCaptureSession(outputSurfaces, new CameraCaptureSession.StateCallback() {
				
				@Override
				public void onConfigured(CameraCaptureSession session) {

					try {
						session.capture(captureBuilder.build(), captureListener, backgroudHandler);
					} catch (CameraAccessException e) {

						e.printStackTrace();
					}
				}
				
				@Override
				public void onConfigureFailed(CameraCaptureSession session) {
					
				}
			}, backgroudHandler);
            
		} catch (CameraAccessException e) {
			e.printStackTrace();
		}

	}

	@Override
	protected void onResume() {
		super.onResume();
		Log.e(TAG, "onResume");
	}

	private void openCamera() {
		
		CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
		Log.e(TAG, "openCamera E");
		try {
			String cameraId = manager.getCameraIdList()[0];
			CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
			StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
			mPreviewSize = map.getOutputSizes(SurfaceTexture.class)[0];
			
			manager.openCamera(cameraId, mStateCallback, null);
		} catch (CameraAccessException e) {
			e.printStackTrace();
		}
		Log.e(TAG, "openCamera X");
	}
	
	private TextureView.SurfaceTextureListener mSurfaceTextureListener = new TextureView.SurfaceTextureListener(){

		@Override
		public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
			Log.e(TAG, "onSurfaceTextureAvailable, width="+width+",height="+height);
			openCamera();
		}

		@Override
		public void onSurfaceTextureSizeChanged(SurfaceTexture surface,
				int width, int height) {
			Log.e(TAG, "onSurfaceTextureSizeChanged");
		}

		@Override
		public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
			return false;
		}

		@Override
		public void onSurfaceTextureUpdated(SurfaceTexture surface) {
			//Log.e(TAG, "onSurfaceTextureUpdated");
		}
		
	};
	
	private CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {

		@Override
		public void onOpened(CameraDevice camera) {

			Log.e(TAG, "onOpened");
			mCameraDevice = camera;
			startPreview();
		}

		@Override
		public void onDisconnected(CameraDevice camera) {

			Log.e(TAG, "onDisconnected");
		}

		@Override
		public void one rror(CameraDevice camera, int error) {

			Log.e(TAG, "onError");
		}
		
	};

	@Override
	protected void onPause() {

		Log.e(TAG, "onPause");		
		super.onPause();
		if (null != mCameraDevice) {
            mCameraDevice.close();
            mCameraDevice = null;
        }
	}

	protected void startPreview() {

		if(null == mCameraDevice || !mTextureView.isAvailable() || null == mPreviewSize) {
			Log.e(TAG, "startPreview fail, return");
			return;
		}
		
		SurfaceTexture texture = mTextureView.getSurfaceTexture();
		if(null == texture) {
			Log.e(TAG,"texture is null, return");
			return;
		}
		
		texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
		Surface surface = new Surface(texture);
		
		try {
			mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
		} catch (CameraAccessException e) {

			e.printStackTrace();
		}
		mPreviewBuilder.addTarget(surface);
		
		try {
			mCameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
				
				@Override
				public void onConfigured(CameraCaptureSession session) {

					mPreviewSession = session;
					updatePreview();
				}
				
				@Override
				public void onConfigureFailed(CameraCaptureSession session) {

					Toast.makeText(MainActivity.this, "onConfigureFailed", Toast.LENGTH_LONG).show();
				}
			}, null);
		} catch (CameraAccessException e) {

			e.printStackTrace();
		}
	}

	protected void updatePreview() {

		if(null == mCameraDevice) {
			Log.e(TAG, "updatePreview error, return");
		}
		
		mPreviewBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
		HandlerThread thread = new HandlerThread("CameraPreview");
		thread.start();
		Handler backgroundHandler = new Handler(thread.getLooper());
		
		try {
			mPreviewSession.setRepeatingRequest(mPreviewBuilder.build(), null, backgroundHandler);
		} catch (CameraAccessException e) {

			e.printStackTrace();
		}
	}
}

Android L Camera2 API sample ver2 - startPreview&takePicture