Android的几种写入文件方式

1.文件（手机内存）

将数据以普通文件的形式保存在 /data/data/com.example.qqLogin/data.txt 中（不需要申请权限）

public static boolean saveUserInfo(String number,String password){
		String path = "/data/data/com.example.qqLogin/data.txt";
		try {
			FileOutputStream fos = new FileOutputStream(path);
			String info = number + "##" + password;
			fos.write(info.getBytes());
			fos.flush();
			fos.close();
			return true;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return false;
	}
	
	public static Map<String,String> getUserInfo(){

		String path = "/data/data/com.example.qqLogin/data.txt";
		try {
			FileInputStream fis = new FileInputStream(path);
			BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
			String text = reader.readLine();
			if(!TextUtils.isEmpty(text)){
				String[] infos = text.split("##");
				Map<String,String> map = new HashMap<String, String>();
				map.put("number",infos[0]);
				map.put("password", infos[1]);
				return map;
			}
			text.split("##");
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

path可用api方式动态获取

		String path = context.getFilesDir().getPath();// data数据目录
		String path = context.getCacheDir().getPath();// data/cache缓存目录

以context打开FileOutputStream，默认路径为 /data/data/<包名>/filename ，具体mode权限见https://blog.youkuaiyun.com/qq_38709999/article/details/81708888

public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		
		// 写数据
		
		// 私有文件
		writeToLocal("private.txt", Context.MODE_PRIVATE);
		// 可读文件
		writeToLocal("readable.txt", Context.MODE_WORLD_READABLE);
		// 可写文件
		writeToLocal("writeable.txt", Context.MODE_WORLD_WRITEABLE);
		// 可读可写文件
		writeToLocal("readable_writeable.txt", Context.MODE_WORLD_READABLE + Context.MODE_WORLD_WRITEABLE);
	}

	private void writeToLocal(String fileName, int mode) {
		try {
			FileOutputStream fos = openFileOutput(fileName, mode);
			fos.write(("第一个程序写的数据: " + fileName).getBytes());
			fos.flush();
			fos.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

 

2.文件（sdcard中）

将数据保存在 /mnt/sdcard/data.txt（需申请权限：android.permission.WRITE_EXTERNAL_STORAGE）

    public static boolean saveUserInfo(Context context, String number, String password) {
		
		try {
			// 判断当前的手机是否有sd卡
			String state = Environment.getExternalStorageState();
			
			if(!Environment.MEDIA_MOUNTED.equals(state)) {
				// 已经挂载了sd卡
				return false;
			}
			
			File sdCardFile = Environment.getExternalStorageDirectory();
			File file = new File(sdCardFile, "data.txt");
			
			FileOutputStream fos = new FileOutputStream(file);
			
			String data = number + "##" + password;
			
			fos.write(data.getBytes());
			
			fos.flush();
			fos.close();
			return true;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return false;
	}
	

	public static Map<String, String> getUserInfo(Context context) {
		
		try {
			// 判断当前的手机是否有sd卡
			String state = Environment.getExternalStorageState();
			
			if(!Environment.MEDIA_MOUNTED.equals(state)) {
				// 已经挂载了sd卡
				return null;
			}
			
			File sdCardFile = Environment.getExternalStorageDirectory();
			
			File file = new File(sdCardFile, "data.txt");
			
			BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
			
			String text = br.readLine();
			
			br.close();
			
			if(!TextUtils.isEmpty(text)) {
				Map<String, String> userInfoMap = new HashMap<String, String>();
				String[] split = text.split("##");
				userInfoMap.put("number", split[0]);
				userInfoMap.put("password", split[1]);
				return userInfoMap;
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

 

3.SharedPreference的使用

将数据以键值对的形式保存在data.xml中，路径为 /data/data/<包名>/shared_prefs/data.xml

public static boolean saveUserInfo(Context context, String number,String password){
		
		try {
			SharedPreferences sp = context.getSharedPreferences("data",Context.MODE_PRIVATE);
			Editor editor = sp.edit();
			
			editor.putString("number", number);
			editor.putString("password", password);
			
			editor.commit();
			return true;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return false;
	}
	
public static Map<String,String> getUserInfo(Context context){

		try {
			SharedPreferences sp = context.getSharedPreferences("data",Context.MODE_PRIVATE);
			
			String number = sp.getString("number", null);
			String password = sp.getString("password", null);
			
			if(!TextUtils.isEmpty(number)&&!TextUtils.isEmpty(password)){
				Map<String,String> map = new HashMap<String, String>();
				map.put("number",number);
				map.put("password", password);
				return map;
			}
			
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

 

4.SQLite数据库

将数据以data.db方式保存在 /data/data/<包名>/databases/data.db 中

1.创建SQLiteOpenHelperDemo 实现虚基类 SQLiteOpenHelper

SQLiteOpenHelperDemo.class

package com.example.DB;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class SQLiteOpenHelperDemo extends SQLiteOpenHelper{

	public SQLiteOpenHelperDemo(Context context) {
		super(context, "data.db", null, 1);
		// TODO Auto-generated constructor stub
	}

	@Override
	public void onCreate(SQLiteDatabase db) {
		// TODO Auto-generated method stub
		String sql = "";
		db.execSQL(sql);
	}

	@Override
	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
		// TODO Auto-generated method stub
		
	}
	
}

 

2.创建实体类（略）

Person.class

 

3.创建dao

PresonDao.class

package com.example.dao;

import java.util.ArrayList;
import java.util.List;

import com.example.DB.SQLiteOpenHelperDemo;
import com.example.pojo.Person;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class PresonDao {

	private SQLiteOpenHelperDemo sQLiteOpenHelperDemo;

	public PresonDao(Context context) {
		sQLiteOpenHelperDemo = new SQLiteOpenHelperDemo(context);
	}
	
	/**
	 * 添加到person表一条数据
	 * @param person
	 */
	public void insert(Person person) {
		SQLiteDatabase db = sQLiteOpenHelperDemo.getWritableDatabase();
		if(db.isOpen()) {	// 如果数据库打开, 执行添加的操作
			
			// 执行添加到数据库的操作
			db.execSQL("insert into person(name, age) values(?, ?);", new Object[]{person.getName(), person.getAge()});
			
			db.close();	// 数据库关闭
		}
	}
	
	/**
	 * 更据id删除记录
	 * @param id
	 */
	public void delete(int id) {
		SQLiteDatabase db = sQLiteOpenHelperDemo.getWritableDatabase();	// 获得可写的数据库对象
		if(db.isOpen()) {	// 如果数据库打开, 执行添加的操作
			
			db.execSQL("delete from person where _id = ?;", new Integer[]{id});
			
			db.close();	// 数据库关闭
		}
	}
	

	/**
	 * 根据id找到记录, 并且修改姓名
	 * @param id
	 * @param name
	 */
	public void update(int id, String name) {
		SQLiteDatabase db = sQLiteOpenHelperDemo.getWritableDatabase();
		if(db.isOpen()) {	// 如果数据库打开, 执行添加的操作
			
			db.execSQL("update person set name = ? where _id = ?;", new Object[]{name, id});
			
			db.close();	// 数据库关闭
		}
	}
	
	public List<Person> queryAll() {
		SQLiteDatabase db = sQLiteOpenHelperDemo.getReadableDatabase();	// 获得一个只读的数据库对象
		if(db.isOpen()) {
			
			Cursor cursor = db.rawQuery("select _id, name, age from person;", null);
			
			if(cursor != null && cursor.getCount() > 0) {
				List<Person> personList = new ArrayList<Person>();
				int id;
				String name;
				int age;
				while(cursor.moveToNext()) {
					id = cursor.getInt(0);	// 取第0列的数据 id
					name = cursor.getString(1);	// 取姓名
					age = cursor.getInt(2);		// 取年龄
					personList.add(new Person(id, name, age));
				}

				db.close();
				return personList;
			}
			db.close();
		}
		return null;
	}
	
	/**
	 * 根据id查询人
	 * @param id
	 * @return
	 */
	public Person queryItem(int id) {
		SQLiteDatabase db = sQLiteOpenHelperDemo.getReadableDatabase();	// 获得一个只读的数据库对象
		if(db.isOpen()) {
			Cursor cursor = db.rawQuery("select _id, name, age from person where _id = ?;", new String[]{id + ""});
			if(cursor != null && cursor.moveToFirst()) {
				int _id = cursor.getInt(0);
				String name = cursor.getString(1);
				int age = cursor.getInt(2);
				db.close();
				return new Person(_id, name, age);
			}
			db.close();
		}
		return null;
	}
}

目录

1.文件（手机内存）

2.文件（sdcard中）

3.SharedPreference的使用

4.SQLite数据库

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