创建sd文件并读取

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.widget.TextView;

/**
 * This activity shows how to write and read data from sdcard
 * @author FaYnaSoft Labs
 *
 */
public class Main extends Activity {
	private static final String APP_TAG = "tag";

	private TextView readOutput;

	@Override
	public void onCreate(final Bundle icicle) {
		super.onCreate(icicle);
		this.setContentView(R.layout.main);

		readOutput = (TextView) findViewById(R.id.output);

		String fileName = "test-" + System.currentTimeMillis() + ".txt";

		// create /sdcard/test_folder
		File sdDir = new File(Environment.getExternalStorageDirectory().getPath());
		if (sdDir.exists() && sdDir.canWrite()) {
			File testDir = new File(sdDir.getAbsolutePath() + "/test_folder");
			testDir.mkdir();
			if (testDir.exists() && testDir.canWrite()) {
				File file = new File(testDir.getAbsolutePath() + "/" + fileName);
				try {
					file.createNewFile();
				} catch (IOException e) {
					Log.e(APP_TAG, "error creating file", e);
				}

				if (file.exists() && file.canWrite()) {
					FileOutputStream fos = null;
					try {
						fos = new FileOutputStream(file);
						fos.write("Hello, World!".getBytes());
					} catch (FileNotFoundException e) {
						Log.e(APP_TAG, "ERROR", e);
					} catch (IOException e) {
						Log.e(APP_TAG, "ERROR", e);
					} finally {
						if (fos != null) {
							try {
								fos.flush();
								fos.close();
							} catch (IOException e) {
							}
						}
					}
				} else {
					Log.e(APP_TAG, "error writing to file");
				}

			} else {
				Log.e(APP_TAG, "ERROR, unable to write to /sdcard/test_folder");
			}
		} else {
			Log.e(APP_TAG, "ERROR, /sdcard path not available");
		}

		// Read file block
		File readFile = new File(sdDir.getPath() + "/test_folder/" + fileName);
		if (readFile.exists() && readFile.canRead()) {
			FileInputStream fis = null;
			try {
				fis = new FileInputStream(readFile);
				byte[] reader = new byte[fis.available()];
				while (fis.read(reader) != -1) {
				}
				readOutput.setText(new String(reader));
			} catch (IOException e) {
				Log.e(APP_TAG, e.getMessage(), e);
			} finally {
				if (fis != null) {
					try {
						fis.close();
					} catch (IOException e) {
					}
				}
			}
		} else {
			readOutput.setText("Unable to read/write sdcard file, see logcat output");
		}
	}
}