assets下的文件复制到SD卡

 由于assets和res下的文件都只可以读不可以写，那么在程序初始化后，将后期需要使用并且需要修改的文件复制到SD卡。下面代码提供一个工具类，将assets下的任意资源复制到SD卡下。

assets下的资源如下图：

下面是工具类： 
AssetsCopyTOSDcard .java

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

import android.content.Context;
import android.content.res.AssetManager;
import android.os.Environment;

public class AssetsCopyTOSDcard {
     Context context;

    public AssetsCopyTOSDcard(Context context) {
        super();
        this.context = context;
    }

    /**
     * @param context
     * @param assetpath  asset下的路径
     * @param SDpath     SDpath下保存路径
     */
    public void AssetToSD(String assetpath,String SDpath ){

        AssetManager asset=context.getAssets();
        //循环的读取asset下的文件，并且写入到SD卡
        String[] filenames=null;
        FileOutputStream out = null;
        InputStream in=null;
        try {
            filenames = asset.list(assetpath);
            if(filenames.length>0){//说明是目录
                //创建目录
                getDirectory(assetpath);

                for(String fileName:filenames){
                    AssetToSD(assetpath+"/"+fileName, SDpath+"/"+fileName);
                }
            }else{//说明是文件，直接复制到SD卡
                File SDFlie=new File(SDpath);
                String  path=assetpath.substring(0, assetpath.lastIndexOf("/"));
                getDirectory(path);

                if(!SDFlie.exists()){
                    SDFlie.createNewFile();
                }
                //将内容写入到文件中
                in=asset.open(assetpath);
                out= new FileOutputStream(SDFlie);
                byte[] buffer = new byte[1024];
                int byteCount=0;
                while((byteCount=in.read(buffer))!=-1){
                    out.write(buffer, 0, byteCount);
                }
                out.flush();
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            try {
                out.close();
                in.close();
                asset.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }
    }
    //分级建立文件夹
    public void getDirectory(String path){
        //对SDpath进行处理，分层级建立文件夹
        String[]  s=path.split("/");
        String str=Environment.getExternalStorageDirectory().toString();
          for (int i = 0; i < s.length; i++) {
            str=str+"/"+s[i];
            File file=new File(str);
            if(!file.exists()){
                file.mkdir();
            }
        }

    }
}

MainActivity .java

import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.view.Menu;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        String path="aaa/a1.txt";
        AssetsCopyTOSDcard assetsCopyTOSDcard=new AssetsCopyTOSDcard(getApplicationContext());
        assetsCopyTOSDcard.AssetToSD(path,Environment.getExternalStorageDirectory().toString()+"/"+path);
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
}

   测试路径：
   aaa
   Aaa/bbb
   Aaa/bbb/ba.txt
   Aaa/a1.txt

在编程过程中遇到的两个问题：

open failed: ENOENT (No such file or directory)
open failed: EISDIR (Is a directory)

错误修改

if(!SDFlie.exists()){
    SDFlie.createNewFile();
}
//将内容写入到文件中
in=asset.open(assetpath);
out= new FileOutputStream(SDFlie);
byte[] buffer = new byte[1024];
int byteCount=0;
while((byteCount=in.read(buffer))!=-1){
   out.write(buffer, 0, byteCount);
}
out.flush();

修改为：

if(!SDFlie.exists()){
      SDFlie.createNewFile();
      //将内容写入到文件中
      in=asset.open(assetpath);
      out= new FileOutputStream(SDFlie);
      byte[] buffer = new byte[1024];
      int byteCount=0;
      while((byteCount=in.read(buffer))!=-1){
         out.write(buffer, 0, byteCount);
     }
}

out.flush();

因为当文件存在时，不复制。不修改的情况下，out.close();会报空指针异常。

finally{
            try {
                out.close();
                in.close();
                asset.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

修改为：

finally{
            try {
                if(out!=null){
                    out.close();
                    out=null;
                    }
                if(in!=null){
                    in.close();
                    in=null;
                    }
                /**
                 * 关闭报错，java.lang.RuntimeException:
                 * Unable to start activity ComponentInfo
                 * {com.example.wealth/com.example.wealth.UI.main}:
                 * java.lang.RuntimeException: Assetmanager has been closed
                 */
//              if(asset!=null){
//                  asset.close();
//                  asset=null;
//                  }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

转: https://blog.csdn.net/qq_17326933/article/details/48450487