SD 卡读写程序

Environment 类位于 android.os 包中，是用于检验和获取手机 SD 卡状态、根路径等信息的工具类。Environment 类中的方法都是静态方法，可以直接调用。

SD 卡读写操作一般需要 4 个步骤：

1、判断 SD 卡状态。Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED) 值为 Ture。

2、获取根路径。Environment.getExternalStorageDirectory()。

3、创建文件夹。File dir = new File(sdRoot,dirName);

4、I/O 读写操作。

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.sql.Statement;

import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.view.Menu;
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 implements OnClickListener{
    
    EditText et1,et2;
    Button b1,b2;
    TextView tv1;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        setContentView(R.layout.activity_main);
        et1 = (EditText) findViewById(R.id.et_name);
        et2 = (EditText) findViewById(R.id.et_pwd);
        tv1 = (TextView) findViewById(R.id.content);
        b1 = (Button) findViewById(R.id.bt_save);
        b2 = (Button) findViewById(R.id.bt_read);
        b1.setOnClickListener(this);
        b2.setOnClickListener(this);
    }
    
    @Override
    public void onClick(View view) {
        
        switch(view.getId()){
        case R.id.bt_save:
            save("/contract/data","cd.txt");
            et1.setText("");
            et2.setText("");
            break;
        case R.id.bt_read:
            read("/contract/data","cd.txt");
            break;
        }
    }
    
    // 读取文件
    private void read(String dirName, String fileName) {
        
        // 判断 SD 状态是否可用
        if(!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
            Toast.makeText(this, "SD卡状态异常", Toast.LENGTH_LONG).show();
            return;
        }
        
        // 获取 SD 卡根路径
        File sdRoot = Environment.getExternalStorageDirectory();
        File file = new File(sdRoot.getAbsolutePath() + dirName, fileName);
        if(!file.exists()){
            Toast.makeText(this, "联系人数据不存在", Toast.LENGTH_LONG).show();
            return;
        }
        
        BufferedReader br = null;
        try {
            br = new BufferedReader(new FileReader(file));
            String ln = null;
            tv1.setText("");
            while((ln = br.readLine())!=null){
                tv1.append(ln+"\n");
            }
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            if(br != null)
                try {
                    br.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
        }
    }
    
    // 保存文件
    private void save(String dirName,String fileName) {
        
        // 判断 SD 状态是否可用
        if(!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
            Toast.makeText(this, "SD卡状态异常", Toast.LENGTH_LONG).show();
            return;
        }
        // 获取 SD 卡根路径
        File sdRoot = Environment.getExternalStorageDirectory();
        // 创建文件夹
        File dir = new File(sdRoot,dirName);
        if(!dir.exists()){
            dir.mkdirs();
        }
        // 创建文件，并写入数据
        File file = new File(dir,fileName);
        PrintWriter pw = null;
        try {
            if(!file.exists()){
                file.createNewFile();
            }
            pw = new PrintWriter(new FileOutputStream(file,true));
            pw.println("好友姓名:" + et1.getText().toString() + "  联系方式：" + et2.getText().toString());
            pw.flush();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            if(pw!=null)pw.close();
        }
    }
}

查看数据存储 DDMS/Fileexplorer

mnt/sdcard/contract/data/cd.txt

【注】

1、应用程序安装路径下存储文件不宜过大，对应需要下载的文件（如音乐、视频等）应该存放在 SD 卡中。

2、使用 SD 卡前需要检验 SD 卡的状态。

3、添加权限。<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

4、封装成一个简单的SD 卡数据存储操作类。

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;

import android.os.Environment;
import android.util.Log;

/*
 * 用于向 sdcard 保存数据
 * */
public class SaveDataSDCard {
    
    final static String T = "Tag";
    
    // 获取 SdCard 根路径
    public File getRoot(){
        
        if(Environment.getExternalStorageState()
                .equalsIgnoreCase(Environment.MEDIA_REMOVED)){
            Log.i(T, "Sd不存在");
            return null;
        }
        return Environment.getExternalStorageDirectory();
    }
    
    // 创建文件夹
    public File createDir(String dirStr){
        
        File dir = new File(getRoot(),dirStr);
        if(!dir.exists()){
            dir.mkdirs();
        }
        return dir;
    }
    
    // 创建文件
    public File createFile(String filePath,String fileName){
        
        File dir = createDir(filePath);
        File file = new File(dir,fileName);
        
        try {
            if(!file.exists()){
                file.createNewFile();
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return file;
    }
    
    /* 向指定文件中写入数据,数据位一个字符串
     * path: 文件路径
     * fileName：文件名
     * content：待写入字符串
     * */
    public File writeData(String path,String fileName,String content){
        
        File file = createFile(path,fileName);
        if(file == null) return null;
        PrintWriter pw = null;
        boolean r = false;
        
        try {
            pw = new PrintWriter(file);
            pw.println(content);
            pw.flush();
            r = true;
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            pw.close();
        }
        return file;
    }
    
    /* 向指定文件中写入数据,数据是一个输入流
     * path:文件路径
     * fileName：文件名
     * is：输入流
     * */
    public File writeData(String path,String fileName,InputStream is){
        
        File file = createFile(path,fileName);
        if(file == null) return null;
        FileOutputStream fos = null;
        byte buffer[] = new byte[1024*4];
        int count;
        
        try {
            fos = new FileOutputStream(file);
            while( (count=is.read(buffer))>0){
                fos.write(buffer, 0, count);
            }
            fos.flush();
        } catch (FileNotFoundException e) {            
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            if(fos != null)
                try {
                    fos.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
        }
        return file;
    }
}