android 开发-文件存储之读写sdcard

　　android提供对可移除的外部存储进行文件存储。在对外部sdcard进行调用的时候首先要调用Environment.getExternalStorageState()检查sdcard的可用状态。通过Environment.getExternalStorageDirectory()得到Sdcard的路径。文件写入外部存储需要添加对sdcard的授权

　　<!-- 写sdcard需要添加写sdcard的授权 -->
　　<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

　　boolean mExternalStorageAvailable = false;
　　boolean mExternalStorageWriteable = false;
　　String state = Environment.getExternalStorageState();

　　if (Environment.MEDIA_MOUNTED.equals(state)) {
 　　   // We can read and write the media
   　　 mExternalStorageAvailable = mExternalStorageWriteable = true;
　　} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
 　　   // We can only read the media
　　    mExternalStorageAvailable = true;
 　　   mExternalStorageWriteable = false;
　　} else {
 　　   // Something else is wrong. It may be one of many other states, but all we need
 　　   //  to know is we can neither read nor write
　　    mExternalStorageAvailable = mExternalStorageWriteable = false;
　　}
android学习过程中的示例如下：
　　文件读写工具类：
　　

package com.example.android_data_storage_sdcard.file;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import android.os.Environment;
import android.util.Log;
/**
 * @author xiaowu
 * @note  文件存储之外部存储（sdcard存储）。
 *         外部存储不需要context        
 */
public class FileUitls {
    private final String TAG = "FileUtil";

    /**
     * 保存文件至外部存储的SD卡
     * @param fileName
     * @param mode
     * @param data
     * @return 是否存储内容到sdcard成功
     */
    public boolean saveFileToSdcard(String fileName,  byte[] data) {
        boolean flag = false;
        // 判断sdcard的状态
        String state = Environment.getExternalStorageState();
        // 获取sdcard的根目录 /mnt/sdcard/...
        File root = Environment.getExternalStorageDirectory();
        FileOutputStream outputStream = null;
        // Environment.MEDIA_MOUNTED表示SD卡挂载在手机上并可以读写
        if (Environment.MEDIA_MOUNTED.equals(state)) {
            // 在sdcard的根目录下创建文件
            File file = new File(root, fileName);
            try {
                outputStream = new FileOutputStream(file);
                outputStream.write(data, 0, data.length);
                flag = true ;
            } catch (FileNotFoundException e) {
                Log.i(TAG, "文件未找到异常！");
            } catch (Exception e) {
                Log.i(TAG, "写文件发生异常");
            } finally {
                if (outputStream != null) {
                    try {
                        outputStream.close();
                    } catch (IOException e) {
                        Log.i(TAG, "关闭IO流发生异常!");
                    }
                }
            }
        }
        return flag;
    }
    /**
     * 从sdcard中读文件
     * @param fileName
     * @return 文件内容
     */
    public String  readFromSdcard(String fileName){
        String  str = "" ;
        FileInputStream inputStream = null;
        String state = Environment.getExternalStorageState();
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        try {
            if (Environment.MEDIA_MOUNTED.equals(state)) {
                //获取Sdcard路径
                File root = Environment.getExternalStorageDirectory();
                File file = new File(root.getAbsolutePath(),fileName);
                if(file.exists()){
                    inputStream = new FileInputStream(file);
                    int len = 0 ;
                    byte[] data = new byte[1024];
                    while ((len = inputStream.read(data)) != -1) {
                        byteArrayOutputStream.write(data, 0, len);
                    }
                    return new String(byteArrayOutputStream.toByteArray());
                }
            }
        } catch (Exception e) {
            Log.i(TAG, "文件读取异常！");
        }finally{
            if(inputStream != null){
                try {
                    inputStream.close();
                } catch (IOException e) {
                    Log.i(TAG, "关闭流异常！");
                }
            }
        }
        return str ;
    }
}

　　Junit单元测试类：

　　单元测试类必须继承自AndroidTestCase，并在资源清单文件中添加单元测试包  <uses-library android:name="android.test.runner"/>,并添加单元测试目标包

　　<!-- 引入单元测试目标包 -->
　　<instrumentation
　　　　android:name="android.test.InstrumentationTestRunner"
　　　　android:targetPackage="com.example.android_data_storage_sdcard" >
　　</instrumentation>

package com.example.android_data_storage_sdcard;

import android.test.AndroidTestCase;

import com.example.android_data_storage_sdcard.file.FileUitls;

public class MyTest extends AndroidTestCase {
    
    public void test() {
        FileUitls fileUitls = new FileUitls();
        fileUitls.saveFileToSdcard("keji.txt", "橘子洲头".getBytes());
    }
}