将数据保存的SDCard前需要先声明权限

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

    <uses-sdk
        android:minSdkVersion="14"
        android:targetSdkVersion="17" />

    <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>
    <!-- 在SDCard中创建和删除文件权限-->
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
    <!-- 往SDCard写入数据的权限 -->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>"

</manifest>

<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.file.MainActivity" >

    <TextView 
        android:id="@+id/textView1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="文件名称"/>
    <EditText 
        android:id="@+id/fileName"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/textView1"/>
    <TextView 
        android:id="@+id/textView2"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/fileName"
        android:text="文本内容"/>
    <!-- 输入yu最少显示3行 -->
    <EditText 
        android:id="@+id/content"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/textView2"
        android:minLines="3"/>
    <Button 
        android:id="@+id/save"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/content"
        android:text="保存"/>
    <TextView 
        android:id="@+id/fileContent"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/save"
        android:text="您输入的内容:"/>
</RelativeLayout>

package com.example.service;

import java.io.File;
import java.io.FileOutputStream;

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

public class FileService {

    private Context context;
    public FileService(Context context){
    	this.context = context;
    }
    public void saveToSDCard(String fileName,String content){
    	/*
    	 * 第一个参数:文件保存的路径，即SDCard的路径
    	 * 第二个参数:保存的文件名
    	 */
    //	File file = new File("/mnt/sdcard",fileName);
    	File file = new File(Environment.getExternalStorageDirectory(),fileName);
    	//SDCard的文件会保存在mnt目录的sdcard文件夹下。SDCard中的数据不受权限控制，可以被任何应用访问
    	//最好不要用SDCard的绝对路径/sdcard,可能会随版本的变化不同
    	FileOutputStream outStream;
		try {
			outStream = new FileOutputStream(file);
	    	outStream.write(content.getBytes());
	    	outStream.close();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
    }
}

package com.example.filesavetosdcard;

import com.example.service.FileService;
import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {

	private EditText fileName;
	private EditText content;
	private Button save;
	private TextView fileContent;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		fileName = (EditText) findViewById(R.id.fileName);
		content = (EditText) findViewById(R.id.content);
		save = (Button) findViewById(R.id.save);
		fileContent = (TextView) findViewById(R.id.fileContent);
		save.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				FileService service = new FileService(getApplicationContext());
				//如果手机没有SDCard或SDCard设置了保护权限，我们是无法访问
				//SDCard的，所以在操作前应先判断SDCard的状态
				if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
					service.saveToSDCard(fileName.getText().toString(),content.getText().toString());
					Toast.makeText(getApplicationContext(), "保存成功", Toast.LENGTH_SHORT).show();
					fileContent.setText("您输入的内容:" + content.getText().toString());
				}else{
					Toast.makeText(getApplicationContext(), "SDCard不存在或写保护", Toast.LENGTH_SHORT).show();
				}
			}
		});
	}
}

点击保存，数据以文件形式保存在sdcard目录下

将myfile导出以记事本方式打开

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将数据保存的SDCard