android学习笔记五—android的存储2 文件的读取与写入

一，data/data/{包名}/files文件夹下的文件读取和写入

在此目录下并不需要做太多处理，只要知道文件名就可以进行读写

//读取文件函数public String readInStream(Context context,String FileName) throws IOException{        FileInputStream in=context.openFileInput(FileName);             //获取文件长度        int length=in.available();        byte [] bytes = new byte[length];        try{            in.read(bytes);        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        String str="";        //解码，需要选择文件对应的格式，否则可能出现乱码等问题        str = EncodingUtils.getString(bytes, "UTF-8");         in.close();        return str;    }    //写入文件函数    public void writeInStream(Context context,int mode,String WantWrite,String FileName) throws IOException{         FileOutputStream out=context.openFileOutput(FileName, mode);         out.write(WantWrite.getBytes());         out.close();    }

二、读取resource/raw文件夹下的文件
需要通过getResources来获得文件

public String readrawInStream(Context context) throws IOException{        InputStream in=context.getResources().openRawResource(R.raw.text);        int length=in.available();        byte [] bytes = new byte[length];        try{            in.read(bytes);        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        String str="";        str = EncodingUtils.getString(bytes, "UTF-8");         in.close();        return str;    }

三，读写SD卡中文件
SD卡中的文件因为存于SD中，所以处理上稍有不同，需要先判断机器上是否插有SD卡，并且是否具有访问权限，之后才能访问文件，下面来介绍一下完整步骤
1.设置SD卡访问权限，毋庸置疑，没有权限是不可能访问成功的，所以需要在入口xml中注册权限，注册方法如代码：

<!-- SD卡创建或删除权限 --><uses-permission android:name="android.permission.MOUNT_FORMAT_FILESYSTEMS"/><!-- SD卡写入权限 --><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>

2.访问之前需要判断机器是否具有sd卡条件，没有自然就不能访问

if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){}

3.获取SD卡目录，并创建文件

if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){            //获取sD卡目录            File SdCarddirectory=Environment.getExternalStorageDirectory();            //创建文件            File Savefilename=new File(SdCarddirectory,fileName);            try{                //创建新文件                Savefilename.createNewFile();               }catch(IOException e){                Toast.makeText(FileDemo.this, e.getMessage(),Toast.LENGTH_LONG).show();            }            FileOutputStream out=new FileOutputStream(Savefilename);            out.write(wantWrite.getBytes());            out.close();        }else{            Toast.makeText(FileDemo.this, "no such file",Toast.LENGTH_LONG).show();        }

文件操作示例代码

FileDemo.javapackage com.example.ui_demo;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.util.List;import org.apache.http.util.EncodingUtils;import android.app.Activity;import android.app.TabActivity;import android.content.Context;import android.content.SharedPreferences;import android.content.SharedPreferences.Editor;import android.graphics.Color;import android.os.Bundle;import android.os.Environment;import android.view.LayoutInflater;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.AdapterView;import android.widget.AdapterView.OnItemSelectedListener;import android.widget.ArrayAdapter;import android.widget.BaseAdapter;import android.widget.Button;import android.widget.EditText;import android.widget.Spinner;import android.widget.TabHost;import android.widget.Toast;import android.widget.TabHost.OnTabChangeListener;public class FileDemo extends Activity {    private String []str={"Mode_Private","Mode_Append","Mode_WorldRead","Mode_WorldWrite"};    private Spinner sp;    private ArrayAdapter<String> arrayAdapter;    private int mySelected=-1;    private Button write;    private Button read;    private Button writeSD;    private Button readSD;    private Button rawread;    private SharedPreferences share;    private EditText name;    private EditText id;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_file_demo);        sp=(Spinner)this.findViewById(R.id.typeFile);        write=(Button)this.findViewById(R.id.writefile);        read=(Button)this.findViewById(R.id.readfile);        writeSD=(Button)this.findViewById(R.id.writeSD);        readSD=(Button)this.findViewById(R.id.readSD);        rawread=(Button)this.findViewById(R.id.rawread);        arrayAdapter=new ArrayAdapter<String>(FileDemo.this,android.R.layout.simple_spinner_item, str);        //arrayAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);        sp.setAdapter(arrayAdapter);        sp.setOnItemSelectedListener(new OnItemSelectedListener(){            @Override            public void onItemSelected(AdapterView<?> arg0, View arg1,                    int position, long id) {                // TODO Auto-generated method stub                String str=arg0.getItemAtPosition(position).toString();                if(str=="Mode_Private"){                   mySelected=Context.MODE_PRIVATE;                }else if(str=="Mode_Append"){                    mySelected=Context.MODE_APPEND;                }else if(str=="Mode_WorldRead"){                    mySelected=Context.MODE_WORLD_READABLE;                }else if(str=="Mode_WorldWrite"){                    mySelected=Context.MODE_WORLD_WRITEABLE;                }else{                    mySelected=-1;                }            }            @Override            public void onNothingSelected(AdapterView<?> arg0) {                // TODO Auto-generated method stub                mySelected=-1;            }        });        Mybutton m=new Mybutton();        write.setOnClickListener(m);        read.setOnClickListener(m);        rawread.setOnClickListener(m);        readSD.setOnClickListener(m);        writeSD.setOnClickListener(m);    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        // Inflate the menu; this adds items to the action bar if it is present.        getMenuInflater().inflate(R.menu.file_demo, menu);        return true;    }    @Override    public boolean onOptionsItemSelected(MenuItem item) {        // Handle action bar item clicks here. The action bar will        // automatically handle clicks on the Home/Up button, so long        // as you specify a parent activity in AndroidManifest.xml.        int id = item.getItemId();        if (id == R.id.action_settings) {            return true;        }        return super.onOptionsItemSelected(item);    }    //读取文件函数    public String readInStream(Context context,String FileName) throws IOException{        FileInputStream in=context.openFileInput(FileName);        int length=in.available();        byte [] bytes = new byte[length];        try{            in.read(bytes);        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        String str="";        str = EncodingUtils.getString(bytes, "UTF-8");         in.close();        return str;    }    public String readrawInStream(Context context) throws IOException{        InputStream in=context.getResources().openRawResource(R.raw.text);        int length=in.available();        byte [] bytes = new byte[length];        try{            in.read(bytes);        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        String str="";        str = EncodingUtils.getString(bytes, "UTF-8");         in.close();        return str;    }    //写入SD卡    public void writeSDInStream(String fileName,String wantWrite) throws IOException{        //判断SD卡是否存在        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){            //获取sD卡目录            File SdCarddirectory=Environment.getExternalStorageDirectory();            //创建文件            File Savefilename=new File(SdCarddirectory,fileName);            try{                Savefilename.createNewFile();               }catch(IOException e){                Toast.makeText(FileDemo.this, e.getMessage(),Toast.LENGTH_LONG).show();            }            FileOutputStream out=new FileOutputStream(Savefilename);            out.write(wantWrite.getBytes());            out.close();        }else{            Toast.makeText(FileDemo.this, "no such file",Toast.LENGTH_LONG).show();        }    }    //读取SD卡    public String readSDInStream(String fileName) throws IOException{        //判断SD卡是否存在        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){            //获取sD卡目录            File SdCarddirectory=Environment.getExternalStorageDirectory();            File readfile=new File(SdCarddirectory,fileName);            FileInputStream in = new FileInputStream(readfile);            int length=in.available();            byte []bytes=new byte[length];            in.read(bytes);            String str=EncodingUtils.getString(bytes, "UTF-8");                     return str;        }else{            return "fail";        }    }    //写入文件函数    public void writeInStream(Context context,int mode,String WantWrite,String FileName) throws IOException{         FileOutputStream out=context.openFileOutput(FileName, mode);         out.write(WantWrite.getBytes());         out.close();    }    public class Mybutton implements OnClickListener{        @Override        public void onClick(View vi) {            // TODO Auto-generated method stub            if(vi==write){                if(mySelected!=-1){                Context context=FileDemo.this;                try {                    //context.openFileOutput("text.txt",Context.MODE_APPEND);                    writeInStream(FileDemo.this,Context.MODE_APPEND,"lianggong zhazha","text.txt");                } catch (FileNotFoundException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                } catch (IOException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }                }else{                    Toast.makeText(FileDemo.this, "未选择type",Toast.LENGTH_LONG).show();                }            }else if(vi==read){                if(mySelected!=-1){                    Context context=FileDemo.this;                    try {                        //context.openFileOutput("text.txt",Context.MODE_APPEND);                        String str="";                        str = readInStream(FileDemo.this,"text.txt");                         Toast.makeText(FileDemo.this, str,Toast.LENGTH_LONG).show();                    } catch (FileNotFoundException e) {                        // TODO Auto-generated catch block                        e.printStackTrace();                    } catch (IOException e) {                        // TODO Auto-generated catch block                        e.printStackTrace();                    }                }else{                    Toast.makeText(FileDemo.this, "未选择type",Toast.LENGTH_LONG).show();                }            }else if(vi==rawread){                try {                    //context.openFileOutput("text.txt",Context.MODE_APPEND);                                   String str="";                    str = readrawInStream(FileDemo.this);                     Toast.makeText(FileDemo.this, str,Toast.LENGTH_LONG).show();                } catch (FileNotFoundException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                } catch (IOException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }            }else if(vi==readSD){                String str="";                try {                    str=readSDInStream("text.txt");                    Toast.makeText(FileDemo.this, str,Toast.LENGTH_LONG).show();                } catch (IOException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }            }else if(vi==writeSD){               try {                writeSDInStream("text.txt","lianggong zhazha gang");            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }            }        }    }}

FileDemo.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    android:paddingBottom="@dimen/activity_vertical_margin"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    tools:context=".FileDemo" >    <TextView        android:id="@+id/NameFile"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="Name:" >    </TextView>    <EditText        android:id="@+id/editNameFile"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="清输入数值" >    </EditText>        <TextView        android:id="@+id/idFile"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="id:" >    </TextView>    <EditText        android:id="@+id/editidFile"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="清输入数值" >    </EditText>    <Spinner        android:id="@+id/typeFile"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:spinnerMode="dropdown" >    </Spinner>    <TableLayout        android:layout_width="wrap_content"        android:layout_height="wrap_content" >    <TableRow >           <Button        android:id="@+id/rawread"        android:text="读取raw"        android:layout_width="wrap_content"        android:layout_height="wrap_content">    </Button>    </TableRow>     <TableRow >    <Button          android:id="@+id/writefile"        android:text="写入"        android:layout_width="wrap_content"        android:layout_height="wrap_content">    </Button>     </TableRow>      <TableRow>     <Button          android:id="@+id/readfile"        android:text="读取"        android:layout_width="wrap_content"        android:layout_height="wrap_content">    </Button>     </TableRow>          <TableRow >    <Button          android:id="@+id/writeSD"        android:text="写入SD"        android:layout_width="wrap_content"        android:layout_height="wrap_content">    </Button>     </TableRow>      <TableRow>     <Button          android:id="@+id/readSD"        android:text="读取SD"        android:layout_width="wrap_content"        android:layout_height="wrap_content">    </Button>     </TableRow>    </TableLayout></LinearLayout>