package com.itheima.writesd;

import java.io.File;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

import android.app.Activity;

import android.os.Bundle;

import android.os.Environment;

import android.view.View;

import android.widget.Toast;

/**

 * 写sd卡一定记得添加权限

 */

public class MainActivity extends Activity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

    }

    /**

     * 模拟向sd卡写一个视频文件.

     */

    public void click(View view) {

        // 检查的sd卡的状态是否被拔出或者是不可用

        if (Environment.getExternalStorageState().equals(

                Environment.MEDIA_MOUNTED)) {

            File sdFile = Environment.getExternalStorageDirectory();// 外部存储空间

            long sdsize = sdFile.getFreeSpace();

            if (sdsize >5* 1024 * 1024) {

                File file = new File(Environment.getExternalStorageDirectory(),//根目录，mnt/sdcard/hlw.3gp

                        System.currentTimeMillis()+"hlw.3gp");//空文件

                try {

                    FileOutputStream fos = new FileOutputStream(file);//文件输出流来写文件

                    byte[] buffer = new byte[1024];//1K,空数据

                    for (int i = 0; i < 5*1024; i++) {//hlw.3gp为5M的空数据文件

                        fos.write(buffer);

                    }

                    fos.close();

                } catch (Exception e) {

                    e.printStackTrace();

                }

            }else{

                Toast.makeText(this, "sd卡空间不足", 0).show();

            }

        } else {

            Toast.makeText(this, "sd卡被拔出或者是不可用", 0).show();

        }

    }

}

清单文件：

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

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

package com.itheima.haker;

import java.io.BufferedReader;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.InputStreamReader;

import android.app.Activity;

import android.os.Build;

import android.os.Bundle;

import android.view.View;

import android.widget.Toast;

public class MainActivity extends Activity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

    }

    public void click(View view){

        try {

            File file = new File("/data/data/com.itheima.createfile/files/haha.txt");//内部存储目录

            FileInputStream fis = new FileInputStream(file);//文件输入流

            BufferedReader br = new BufferedReader(new InputStreamReader(fis));//输入流进行包装

            String line = br.readLine();//读取第一行

            Toast.makeText(this, line, 0).show();

        } catch (Exception e) {

            Toast.makeText(this, "读取失败", 0).show();//文件在手机内部存储空间默认是私有的，别的应用程序是不能访问的，也可以改为公有。

            e.printStackTrace();

        }

    }

}