Android外部SD卡的读取

 package com.kevin.writeorreadfile1_1;

 import android.app.Activity;
 import android.bluetooth.le.ScanFilter;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.media.MediaScannerConnection;
 import android.os.Bundle;
 import android.os.Environment;
 import android.util.Log;
 import android.view.View;
 import android.widget.Button;
 import android.widget.ImageView;
 import android.widget.Toast;

 import java.io.BufferedInputStream;
 import java.io.BufferedOutputStream;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.Scanner;

 /**
  * 保存并读取数据
  * 1.确保外部SD卡可用Environment.getExternalStorageState()；
  * 2.获取SD卡的根路径
  * 3.写入权限
  * <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
  * <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"></uses-permission>
  * 4.读取
  */
 public class MainActivity extends Activity implements View.OnClickListener {
     private boolean state = true;
     private  File file;
     private ImageView img;
     private Button keepBtn,readBtn;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         //初始化控件
         keepBtn = (Button) findViewById(R.id.btn_keep_file);
         readBtn = (Button) findViewById(R.id.btn_read_file);
         img = (ImageView) findViewById(R.id.out_img);

         //点击事件
         keepBtn.setOnClickListener(this);
         readBtn.setOnClickListener(this);

         //确保SD卡可用
         String storageState = Environment.getExternalStorageState();//获取SD卡的状态
         if(storageState.equals(Environment.MEDIA_MOUNTED)){
             Log.i("TAG","当前SD卡可用");
         }else {
             state = false;
         }
     }

     @Override
     public void onClick(View view) {
             switch (view.getId()){
                 case R.id.btn_keep_file://点击保存
                     if(state){
                         saveImg();
                     }
                     break;
                 case R.id.btn_read_file://点击读取
                     if(state){
                         showImg();
                     }
                     break;
             }
     }
     //
     public void saveImg(){
         BufferedInputStream is = null;
         BufferedOutputStream os = null;
         try {
             File storageDirectory = Environment.getExternalStorageDirectory();
             file = new File(storageDirectory,"YangKai.jpg");
             //读取项目中的图片
             InputStream inputStream = getResources().openRawResource(R.drawable.yangkai_photo);
             OutputStream outputStream = new FileOutputStream(file);
             //缓存机制
             is = new BufferedInputStream(inputStream);
             os = new BufferedOutputStream(outputStream);
             //读写操作
             int length = 0 ;
             byte[] bytes = new byte[1024];
             while ((length = is.read(bytes)) != -1){
                 os.write(bytes,0,length);
                 os.flush();//刷新操作
             }
             Toast.makeText(this,"图片已保存",Toast.LENGTH_SHORT).show();
             ScanFile(file.getPath());
         } catch (FileNotFoundException e) {
             e.printStackTrace();
         } catch (IOException e) {
             e.printStackTrace();
         }finally {
             if ( is != null){
                 try {
                     is.close();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
             }
             if (os != null){
                 try {
                     os.close();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
             }
         }
     }

     //扫描进入图片
     private void ScanFile(String path) {

         MediaScannerConnection.scanFile(this,new String[]{path},null,null);
     }

     //显示图片
     public void showImg(){
         //从文件中读取出来
         Bitmap bitmap = BitmapFactory.decodeFile(file.getPath());
         img.setImageBitmap(bitmap);
     }
 }