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