Android中数据存储——文件存储数据

文件操作所需要的权限：

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

package com.example.administrator.myapplication;

import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.OutputStreamWriter;

/**
 * AndroidManifest添加写入数据的权限
 * Andriod 23以后，就算是添加权限也需要在使用时动态请求，否则文件操作会失败
 * 外部存储：
 * 保存外部SD卡中，使用之前确定SD卡可用
 * 确保当前SD卡可用
 * 获取SD卡的根路径
 * 创建文件对象，由于不同手机SDcard目录不同，
 * 所以我们通过Environment.getExternalStorageDirectory()获得路径。
 */
public class FileoperationActivity extends AppCompatActivity {
    //一级文件夹路径
    public final static String Folder_NAME = Environment.getExternalStorageDirectory() + File.separator + "HelloTest";
    //二级文件夹路径
    public final static String Second_PATH = Folder_NAME + File.separator + "SecondFolder" + File.separator;
    //文件路径
    public static final String FILE_NAME = Folder_NAME + File.separator + "HelloTest.txt";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fileoperation);
        FolderCreate();
        FileCreate();
        FileWrite();
        FileRead();
    }


    /**
     * 文件夹创建
     */
    private void FolderCreate() {
        //mkdirs()可以建立多级文件夹， mkdir()只会建立一级的文件夹
        File dirFirstFolder = new File(Second_PATH);
        if (!dirFirstFolder.exists()) {
            dirFirstFolder.mkdirs();
        }
    }

    /**
     * 文件创建
     */
    private void FileCreate() {
        File file = new File(FILE_NAME);
        if (!file.exists()) {
            try {
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 文件的写入
     */
    private void FileWrite() {
        File file = new File(FILE_NAME);
        if (!file.exists()) {
            try {
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        try {
            FileOutputStream fos = new FileOutputStream(file);
            BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(fos));
            bw.write(System.currentTimeMillis() + "你好啊");
            bw.flush();
            bw.close();
            fos.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * 文件的读取
     */
    private void FileRead() {
        try {
            File file = new File(FILE_NAME);
            BufferedReader br = new BufferedReader(new FileReader(file));
            String readline = "";
            StringBuffer sb = new StringBuffer();
            while ((readline = br.readLine()) != null) {
                System.out.println("readline:" + readline);
                sb.append(readline);
            }
            br.close();
            System.out.println("读取成功：" + sb.toString());
            Toast.makeText(this, sb, Toast.LENGTH_SHORT).show();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Android中数据存储——文件存储数据

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