内存卡操作及文件下载功能的实现

一、权限的获取：

应用程序如要要使用联网功能，或者是操作SD卡，需要在AndroidManifest.xml中配置相应的权限：

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<!-- 联网权限 -->

<uses-permission android:name="android.permission.INTERNET"/>

<!-- SD卡操作权限 -->

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

二、要操作SD卡，首先要读取它在Android操作系统中的路径：

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SDCardPath = Environment.getExternalStorageDirectory() + "/";

三、获取了SD卡的路径之后的操作，同于Java中的文件IO操作，此不赘述。

四、网络操作

1、由URL获取HTTP连接

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import java.net.HttpURLConnection;

import java.net.URL;

url = new URL(strUrl); // 获取URL

// 获取HTTP连接

urlConn = (HttpURLConnection) url.openConnection();

2、由HTTP连接获取输入字节流

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java.io.InputStream = urlConn.getInputStream()

3、其它操作同Java IO操作

五、示例代码：下载一个文本文件在控制行输出其内容，再下载这个文件保存早SD卡下

1、AndroidManifest.xml

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<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="me.bym"

android:versionCode="1"

android:versionName="1.0">

<uses-sdk android:minSdkVersion="4" />

<application android:icon="@drawable/icon" android:label="@string/app_name">

<activity android:name=".DownLoadActivity"

android:label="@string/app_name">

<intent-filter>

<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />

</intent-filter>

</activity>

</application>

<uses-permission android:name="android.permission.INTERNET"/>

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

</manifest>

2、文件操作类FileHelper.java

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package me.bym.utils;

import java.io.File;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import android.os.Environment;

public class FileHelper {

private String SDCardPath = null; // SD卡在Android文件系统中的路径

public String getPath() {

return SDCardPath;

}

/**

* 构造方法，获取SD卡在Android文件系统中的路径

*/

public FileHelper() {

SDCardPath = Environment.getExternalStorageDirectory() + "/";

}

/**

* 在SD卡上创建文件

*

* @param fileName

* 要创建的文件名

* @return 创建得到的文件

*/

public File createSDFile(String fileName) throws IOException {

File file = new File(SDCardPath + fileName);

file.createNewFile();

return file;

}

/**

* 在SD卡上创建目录

*

* @param dirName

* 要创建的目录名

* @return 创建得到的目录

*/

public File createSDDir(String dirName) {

File dir = new File(SDCardPath + dirName);

dir.mkdir();

return dir;

}

/**

* 判断文件是否已经存在

*

* @param fileName

* 要检查的文件名

* @return boolean, true表示存在，false表示不存在

*/

public boolean isFileExist(String fileName) {

File file = new File(SDCardPath + fileName);

return file.exists();

}

/**

* 将一个输入流中的内容写入到SD卡上生成文件

*

* @param path

* 文件目录

* @param fileName

* 文件名

* @param inputStream

* 字节输入流

* @return 得到的文件

*/

public File writeToSDCard(String path, String fileName,

InputStream inputStream) {

File file = null;

OutputStream output = null;

try{

createSDDir(path);

file = createSDFile(path + fileName);

output = new FileOutputStream(file);

byte buffer [] = new byte[4 * 1024];

while((inputStream.read(buffer)) != -1){

output.write(buffer);

}

output.flush();

}

catch(Exception e){

e.printStackTrace();

}

finally{

try{

output.close();

}

catch(Exception e){

e.printStackTrace();

}

}

return file;

}

}

3、HTTP下载操作类HttpDownloadHelper.java

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package me.bym.utils;

import java.io.BufferedReader;

import java.io.File;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.net.HttpURLConnection;

import java.net.URL;

public class HttpDownloadHelper {

private URL url = null;

private HttpURLConnection urlConn = null;

private final int SUCCESS = 1;

private final int EXIST = 0;

private final int ERROR = -1;

/**

* 通过传递一个url下载对应的文本文件。

*

* @param strUrl

* 下载文件的URL地址

* @return 下载得到的文本文件内容字符串

*/

public String textDownload(String strUrl) {

StringBuilder sb = new StringBuilder(512); // 初始化文本内容缓冲区。

String line = null;

BufferedReader br = null;

try {

url = new URL(strUrl); // 获取URL

// 获取HTTP连接

urlConn = (HttpURLConnection) url.openConnection();

br = new BufferedReader(new InputStreamReader(

urlConn.getInputStream()));

while ((line = br.readLine()) != null) {

sb.append(line);

}

} catch (Exception e) {

e.printStackTrace();

} finally {

try {

br.close();

} catch (IOException e) {

e.printStackTrace();

}

}

return sb.toString();

}

/**

* 通过传递一个url下载对应的文件。

*

* @param strUrl

* 下载文件的url地址

* @param path

* 保存文件的路径

* @param fileName

* 保存文件的文件名

* @return SUCCESS:文件下载成功 ERROR:文件下载失败 EXIST:同名文件已存在

*/

public int fileDownload(String strUrl, String path, String fileName) {

FileHelper fileHelper = new FileHelper();

InputStream inputStream = null;

File file = null;

if (fileHelper.isFileExist(path + fileName)) {

return EXIST;

} else {

try {

inputStream = getInputStream(strUrl);

file = fileHelper.writeToSDCard(path, fileName, inputStream);

if (file == null) {

return ERROR;

}

} catch (IOException e) {

e.printStackTrace();

} finally {

try {

inputStream.close();

} catch (IOException e) {

e.printStackTrace();

}

}

}

return SUCCESS;

}

/**

* 通过一个url获取http连接的输入流

*

* @param strUrl

* 目标url

* @return 到该url的http连接的输入流

* @throws IOException

*/

private InputStream getInputStream(String strUrl) throws IOException {

url = new URL(strUrl);

urlConn = (HttpURLConnection) url.openConnection();

InputStream is = urlConn.getInputStream();

return is;

}

}

4、Activity类

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package me.bym;

import me.bym.utils.HttpDownloadHelper;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

public class DownLoadActivity extends Activity {

private Button downloadText = null;

private Button downloadFile = null;

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

downloadText = (Button) findViewById(R.id.downloadText);

downloadText.setOnClickListener(new downTextListener());

downloadFile = (Button) findViewById(R.id.downloadFile);

downloadFile.setOnClickListener(new downFileListener());

}

class downTextListener implements OnClickListener {

@Override

public void onClick(View v) {

HttpDownloadHelper downHelper = new HttpDownloadHelper();

String str = downHelper

.textDownload("http://news.swjtu.edu.cn/shownews-2638.html");

System.out.println(str);

}

}

class downFileListener implements OnClickListener {

@Override

public void onClick(View v) {

HttpDownloadHelper downHelper = new HttpDownloadHelper();

int res = downHelper.fileDownload(

"http://www.swjtu.edu.cn/images/swjtu_title.jpg", "myImg/", "a.html");

switch (res) {

case 0:

System.out.println("文件已存在");

break;

case 1:

System.out.println("文件下载成功");

break;

case -1:

System.out.println("文件下载失败");

break;

}

}

}

}

原文：http://blog.csdn.net/baoyiming1991/article/details/6307373