Android数据存储 与访问操作——存放在SDCard

主要的代码：

MainActivity.java

package cn.bzu.fileoperation;

import java.io.IOException;

import cn.bzu.service.FileService;
import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {
	private FileService fileService;
	private Button saveButton;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		fileService = new FileService(this);
		saveButton = (Button) this.findViewById(R.id.save);
		saveButton.setOnClickListener(new View.OnClickListener() {

			@Override
			public void onClick(View v) {
				EditText fileNameText = (EditText) findViewById(R.id.filename);
				EditText fileContentText = (EditText) findViewById(R.id.filecontent);
				String fileName = fileNameText.getText().toString();
				String fileContent = fileContentText.getText().toString();
				if (Environment.getExternalStorageState().equals(
						Environment.MEDIA_MOUNTED)) {
					try {

						fileService.saveToSDCard(fileName, fileContent);
						Toast.makeText(MainActivity.this, R.string.success,
								Toast.LENGTH_LONG).show();
					} catch (IOException e) {
						e.printStackTrace();
						Toast.makeText(MainActivity.this, R.string.failure,
								Toast.LENGTH_LONG).show();
					}
				}else{
					Toast.makeText(MainActivity.this, R.string.sdcarderror, Toast.LENGTH_LONG).show();
				}
			}
		});
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.activity_main, menu);
		return true;
	}

}

FileService.java

package cn.bzu.service;

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

import android.content.Context;
import android.os.Environment;

public class FileService {

	private Context context;

	public FileService(Context context) {
		super();
		this.context = context;
	}

	/**
	 * 保存文件
	 */
	public void save(String filename, String filecontent) throws IOException {
		// 第1个参数是文件的名称，第2个参数是操作模式
		FileOutputStream fos = context.openFileOutput(filename,
				Context.MODE_WORLD_WRITEABLE + Context.MODE_WORLD_READABLE);
		fos.write(filecontent.getBytes());
		fos.close();
	}

	public void saveToSDCard(String filename, String filecontent)
			throws IOException {
		//绝对路径
		//File file = new File("/mnt/sdcard", filename);
		System.out.println(Environment.getExternalStorageDirectory());
		File file=new File(Environment.getExternalStorageDirectory(),filename);
		FileOutputStream fos = new FileOutputStream(file);// 创建文件输出流
		fos.write(filecontent.getBytes());
		fos.close();
	}

	public String readFile(String filename) throws IOException {
		FileInputStream fis = context.openFileInput(filename);
		int len = 0;
		byte[] buffer = new byte[1024];
		ByteArrayOutputStream baos = new ByteArrayOutputStream();// 往内存中输出数据的
		while ((len = fis.read(buffer)) != -1)// 如果数据量很大，第2次读取的数据有可能会把第1次读取的数据给覆盖掉
		{
			baos.write(buffer, 0, len);
		}

		byte[] data = baos.toByteArray();// 得到内存中的数据 以二进制存放的
		baos.close();
		fis.close();
		return new String(data);// 根据二进制数据转换成所对应的字符串
	}
}

接下来，让我们看一下布局文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/filename" />

    <EditText
        android:id="@+id/filename"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/filecontent" />

    <EditText
        android:id="@+id/filecontent"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:minLines="5" />

    <Button
        android:id="@+id/save"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/save" />

</LinearLayout>

有一点，最好对、FileService进行一下单元测试：

package cn.bzu.service;

import java.io.IOException;

import android.test.AndroidTestCase;

public class FileServiceTest extends AndroidTestCase {
    public void testSave() throws IOException{
    	FileService fileService=new FileService(getContext());
    	fileService.save("file1.txt", "使用文件");
    }
    
    public void testRead() throws IOException{
    	FileService fileService=new FileService(getContext());
    	String content=fileService.readFile("file1.txt");
        System.out.println(content);
    }
    public void testSaveToSDCard()throws IOException{
    	FileService fileService=new FileService(getContext());
    	fileService.saveToSDCard("file2.txt", "文件存到sdcard里");
    }
}

还有一点很重要，就是设置权限：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="cn.bzu.fileoperation"
    android:versionCode="1"
    android:versionName="1.0" >

   

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="15" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <uses-library android:name="android.test.runner" />

        <activity
            android:name=".MainActivity"
            android:label="@string/title_activity_main" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
    <!-- 创建文件删除文件权限 -->
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />
    <!-- 往SDCard写入数据权限 -->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <instrumentation
        android:name="android.test.InstrumentationTestRunner"
        android:targetPackage="cn.bzu.fileoperation" >   
    </instrumentation>
</manifest>

让我们看一下运行图：