android 之数据存储(IO)

android 操作文件分为两种，

  第一种：直接写到手机内存中，手机内存有限。

  第二种：写到手机的内存卡(SD)中，进行操作文件。

  以下分为两种情况的读精心操作，一个简单的demo.在此做一个记录。

 代码。

package com.hkrt.action;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.io.RandomAccessFile;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class IOtestActivity extends Activity {
	public EditText edit;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        edit = (EditText)this.findViewById(R.id.inputEdit);
        Button read = (Button)this.findViewById(R.id.read);
        Button write = (Button)this.findViewById(R.id.write);
        write.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
//				write(edit.getText().toString());
				writeDB(edit.getText().toString());
				Toast.makeText(IOtestActivity.this, "写入成功", 0).show();	
			}
        });
        read.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
//				String str=	read();
				String str=readSD();
				if(str!=null){
					Toast.makeText(IOtestActivity.this, "获取到的值："+str, 0).show();	
				}
				
			}
		});
        
        
    }
  /**从手机内存中读取*/
	private String read() {
		StringBuffer sb = null;
		try {
			FileInputStream fis = openFileInput("info");
			byte[] buff = new byte[8192];
			int hasread = 0;
			sb = new StringBuffer();
			while ((hasread = fis.read(buff)) > 0) {
				sb.append(new String(buff, 0, hasread));
			}

		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return sb.toString();
	}
	  /**写到手机内存中*/
	private void write(String content) {
		FileOutputStream fos = null;
		try {
			fos = openFileOutput("info", Context.MODE_APPEND);
			PrintStream ps = new PrintStream(fos);
			ps.print(content);
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} finally {
			if (fos != null) {
				try {
					fos.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}
	/**从sd卡中取内容*/
	private String readSD(){
		FileInputStream fis=null;
		StringBuffer sb = new StringBuffer("");
		//检测是否有sd卡，有没有对sd卡进行读写的权限
		if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
			File sdCardDir = Environment.getExternalStorageDirectory();//获取到文件的存储位置
			try {
				fis= new FileInputStream(new File(sdCardDir.getCanonicalFile()+"/info2"));
				BufferedReader br = new BufferedReader(new InputStreamReader(fis));
				
				String str=null;
				while((str=br.readLine())!=null){
					sb.append(str);
				}
			} catch (FileNotFoundException e) {
				e.printStackTrace();
			} catch (IOException e) {
				e.printStackTrace();
			}finally{
				if(fis!=null){
					try {
						fis.close();
					} catch (IOException e) {
						e.printStackTrace();
					}
				}
			}
			
		}
		return sb.toString();
		
	}
	/**把内容写到SD卡中*/
	private void writeDB(String str){
		RandomAccessFile random =null;
		if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
			try {
				File sdCardDir = Environment.getExternalStorageDirectory();//获取到文件的存储位置
				File targetFile= new File(sdCardDir+"/info2");
				random=  new RandomAccessFile(targetFile, "rw"); 
				random.seek(targetFile.length());
				random.write(str.getBytes());
			} catch (FileNotFoundException e) {
				e.printStackTrace();
			} catch (IOException e) {
				e.printStackTrace();
			}finally{
				if(random!=null){
					try {
						random.close();
					} catch (IOException e) {
						e.printStackTrace();
					}
				}
			}
		}
	}
}

效果图：

SD