There are many ways to store data, such as database storage, SharedPreferences storage, file storage, etc.;
Here we will introduce the simplest file storage method;
The file storage is simply the IO stream in the general JAVASE, but it is only applied to the Android phone;
1. File storage core code
file storage
(1)FileOutputStream out = context.openFileOutput(String filename,int mode); Obtain the file output stream in mode mode
(2)out.write(byte[]b);
FileOutputStream out = null;
out = context.openFileOutput(filename, Context.MODE_***);
out.write(filecontent.getBytes("UTF-8"));
out.close();
Note: files are stored in /data/data/package/files by default;
file read
(1)FileInputStream in = context.openFileInput(String filename); Get the file stream of a file
(2)int length = in.read(byte[]);
/*
<span style="white-space:pre"> </span> Read a fixed byte each time, and output this byte to the byte output stream. output together
*/
FileInputStream in = null;
ByteArrayOutputStream bout = null;
byte[]buf = new byte[1024];
bout = new ByteArrayOutputStream();
int length = 0;
in = context.openFileInput(filename); //Get the input stream
while((length=in.read(buf))!=-1){
bout.write(buf,0,length);
}
byte[] content = bout.toByteArray();
filecontentEt.setText(new String(content,"UTF-8")); //Set the text box to read content
in.close();
bout.close();
Note: The file of /data/data/package/files will be read by default;
2. Introduction to file mode
1.Context.MODE_PRIVATE: private override mode - rw- rw- ---
Can only be accessed by the current application, and overwrites if written ;
2.Context.MODE_APPEND: private append mode - rw- rw- ---
Accessible only by the current application, and appends if written;
3. Context, MODE_WORLD_READABLE: public read-only mode - rw- rw- r--
can be read by other applications;
4.Context.MODE_WORLD_WRITEABLE: public writable mode - rw- rw- -w-
Can be written by other applications, but not read;
Note that if you want the other to make the file modes superimposed, you can use the plus sign to connect;
比如：Context.MODE_WORLD_READABLE + Context.MODE_WORLD_WRITEABLE 表示其他应用读写；
三、简单应用实例
1.效果图
目标：当点击保存时，将以特定的文件名称和特定的文件内容保存内容，点击读取时，将读取特定的文件的文件内容显示到文件内容文本框；
当点击保存之后，效果如下：
MainActivity.java
package org.xiazdong.file;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends Activity {
private Button saveButton,readButton;
private EditText filenameEt,filecontentEt;
private Context context = this;
private OnClickListener listener = new OnClickListener(){
@Override
public void onClick(View v) {
if(v==saveButton){
String filename = filenameEt.getText().toString();
String filecontent = filecontentEt.getText().toString();
FileOutputStream out = null;
try {
out = context.openFileOutput(filename, Context.MODE_PRIVATE);
out.write(filecontent.getBytes("UTF-8"));
} catch (Exception e) {
e.printStackTrace();
}
finally{
try {
out.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
else if(v==readButton){
String filename = filenameEt.getText().toString(); //获得读取的文件的名称
FileInputStream in = null;
ByteArrayOutputStream bout = null;
byte[]buf = new byte[1024];
bout = new ByteArrayOutputStream();
int length = 0;
try {
in = context.openFileInput(filename); //获得输入流
while((length=in.read(buf))!=-1){
bout.write(buf,0,length);
}
byte[] content = bout.toByteArray();
filecontentEt.setText(new String(content,"UTF-8")); //设置文本框为读取的内容
} catch (Exception e) {
e.printStackTrace();
}
filecontentEt.invalidate(); //刷新屏幕
try{
in.close();
bout.close();
}
catch(Exception e){}
}
}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
saveButton = (Button)this.findViewById(R.id.saveButton);
readButton = (Button)this.findViewById(R.id.readButton);
filenameEt = (EditText)this.findViewById(R.id.filename);
filecontentEt = (EditText)this.findViewById(R.id.filecontent);
saveButton.setOnClickListener(listener);
readButton.setOnClickListener(listener);
}
}
四、将文件保存到SDCard
如果一个文件很大，则不适用于存放在手机的存储中；
如果手机存在sdcard，则sdcard的目录为/mnt/sdcard目录；
步骤1：设置模拟器支持sdcard
此时模拟器已经支持sdcard了；
步骤2：在应用中设置权限
在AndroidManifest.xml中设置：
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"></uses-permission> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
存储到sdcard核心代码：
File f = new File(Environment.getExternalStorageDirectory(),filename);
out = new FileOutputStream(f,true);
out.write(filecontent.getBytes("UTF-8"));
读取sdcard核心代码：
File f = new File(Environment.getExternalStorageDirectory(),filename);
in = new FileInputStream(f);
while((length=in.read(buf))!=-1){
bout.write(buf,0,length);
}
byte[] content = bout.toByteArray();
其实主要就是存储目录问题；
注意：
在Android中1.5、1.6的sdcard目录为/sdcard，而Android2.0以上都是/mnt/sdcard，因此如果我们在保存时直接写具体目录会不妥，因此我们可以使用:
Environment.getExternalStorageDirectory();获取sdcard目录；
建议：
(1) The sdcard storage method cannot be used purely, because if it is impossible to determine whether a mobile phone has an sdcard, if not, other solutions need to be provided, such as
Save to phone storage;
Prompt that there is no sdcard;
can use:
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
//Execute the storage sdcard method
}
else{
//Store to the phone, or prompt
}