Android中SD卡读写操作

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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sdcardif (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sdcardif (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 ;}}

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