SD卡的读写是我们在开发Android 应用程序过程中最常见的操作。下面介绍SD卡的读写操作方式：
1. 获取SD卡的根目录
2. 在SD卡上创建文件夹目录
/**
* 在SD卡上创建目录
*/
public File createDirOnSDCard(String dir)
{
File dirFile = new File(sdCardRoot + File.separator + dir +File.separator);
Log.v("createDirOnSDCard", sdCardRoot + File.separator + dir +File.separator);
dirFile.mkdirs();
return dirFile;
}
3. 在SD卡上创建文件
/**
* 在SD卡上创建文件
*/
public File createFileOnSDCard(String fileName, String dir) throws IOException
{
File file = new File(sdCardRoot + File.separator + dir + File.separator + fileName);
Log.v("createFileOnSDCard", sdCardRoot + File.separator + dir + File.separator + fileName);
file.createNewFile();
return file;
}
4.判断文件是否存在于SD卡的某个目录
/**
* 判断SD卡上文件是否存在
*/
public boolean isFileExist(String fileName, String path)
{
File file = new File(sdCardRoot + path + File.separator + fileName);
return file.exists();
}
5.将数据写入到SD卡指定目录文件
/* 写入数据到SD卡中
*/
public File writeData2SDCard(String path, String fileName, InputStream data)
{
File file = null;
OutputStream output = null;
try {
createDirOnSDCard(path); //创建目录
file = createFileOnSDCard(fileName, path); //创建文件
output = new FileOutputStream(file);
byte buffer[] = new byte[2*1024]; //每次写2K数据
int temp;
while((temp = data.read(buffer)) != -1 )
{
output.write(buffer,0,temp);
}
output.flush();
} catch (Exception e) {
e.printStackTrace();
}
finally{
try {
output.close(); //关闭数据流操作
} catch (Exception e2) {
e2.printStackTrace();
}
}
return file;
}
注意事项
对SD卡的操作，必须要申请权限：
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
详情看这里 https://www.jb51.net/article/34296.htm
注意：不直接进行读出是为了防止打文件操作对内存的消耗，所以用输入流读到硬盘上。
public String readFile(String fileName) throws Exception{
FileInputStream fis = context.openFileInput(fileName);
byte[] bytes = new byte[fis.available()];
fis.read(bytes);
fis.close();
return new String(bytes,"utf-8");
}
当文件很大的时候，byte[]会占用很大的内存。
package cn.itcast.fileio.service;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.os.Environment;
public class SdCardService {
private Context ctx;
public SdCardService(Context ctx) {
this.ctx = ctx;
}
/**
* 写文件入skcard
*/
public void writeToSdCard(String fileName, String cont) {
try {
// 判断是否有挂载sdcard
if (Environment.getExternalStorageState().equals(
Environment.MEDIA_MOUNTED)) {
// 得到sdcar文件目录
File dir = Environment.getExternalStorageDirectory();
File file = new File(dir, "itcast.txt");
FileOutputStream fos = new FileOutputStream(file);
fos.write(cont.getBytes());
fos.close();
}
}
catch (Exception e) {
e.printStackTrace();
}
}
/**
* 读SdCard中的文件
*/
public String readSdCard(String fileName) {
try {
// 判断是否有挂载sdcard
if (Environment.getExternalStorageState().equals(
Environment.MEDIA_MOUNTED)) {
// 得到sdcar文件目录
File dir = Environment.getExternalStorageDirectory();
File file = new File(dir, "itcast.txt");
FileInputStream fis = new FileInputStream(file);
return readIs2String(fis);
}
}
catch (Exception e) {
e.printStackTrace();
}
return null;
}
/**
* 将输入流数据读取到输出流当中
*/
private OutputStream readIs2Os(InputStream is ,OutputStream os){
try {
byte[] bytes = new byte[1024];
int length = 0 ;
while((length = is.read(bytes)) != -1){
os.write(bytes, 0, length);
}
is.close();
os.close();
}
catch (IOException e) {
e.printStackTrace();
}
return os ;
}
/**
* 将输入流数据读取到输出流当中
*/
public byte[] readIs2Bytes(InputStream is){
ByteArrayOutputStream baos = new ByteArrayOutputStream();
readIs2Os(is,baos);
return baos.toByteArray() ;
}
public String readIs2String(InputStream is){
try {
return new String(readIs2Bytes(is),"utf-8");
}
catch (Exception e) {
e.printStackTrace();
}
return null ;
}
public String readIs2String(String fileName){
try {
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
File dir = Environment.getExternalStorageDirectory();
File file = new File(dir,fileName);
FileInputStream is = new FileInputStream(file);
return readIs2String(is);
}
}
catch (Exception e) {
e.printStackTrace();
}
return null ;
}
}
