想把文件保存到SD卡中，一定要知道SD卡的路徑，獲取SD卡路徑：

Environment.getExternalStorageDirectory()

另外，在保存之前要判斷SD卡是否已經安裝好，並且可讀寫：

//判斷SDcard是否存在並且可讀寫
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
                    service.saveToSDCard(filename,filecontent);
                    Toast.makeText(getApplicationContext(), R.
 
string.success, 1).show();
                }else{
                    Toast.makeText(getApplicationContext(), R.string.sdcarderror, 1).show();
                }

實例

1. 下載存文本文件和下載如mp3等大容量的文件

2.代碼編寫

AndroidMainfest.xml中配置

主要是解決網絡權限和寫SDCard的權限

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="
 
http://schemas.android.com/apk/res/android"
    package="com.jingling.practice.downloadtest" >


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

    <application
        android:allowBackup
 
="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        <activity
            android:name=".MainActivity"
            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>

</manifest>

package util;

import android.util.Log;

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;

/**
 * Created by Spring on 2015/11/7.
 * 下載工具類
 */
public class HttpDownloader {
    private URL url = null;
    private final String TAG = "TAG";

    /**
     * 讀取文本文件
     * @param urlStr url路徑
     * @return 文本信息
     * 根據url下載文件，前提是這個文件中的內容是文本，
     * 1.創建一個URL對象
     * 2.通過URL對象，創建一個Http連接
     * 3.得到InputStream
     * 4.從InputStream中得到數據
     */
    public String download(String urlStr) {
        StringBuffer sb = new StringBuffer();
        String line = null;
        BufferedReader bufferedReader = null;

        try {
            url = new URL(urlStr);
            //創建http連接
            HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
            //使用IO流讀取數據
            bufferedReader = new BufferedReader(new InputStreamReader(urlConn.getInputStream()));
            while ((line = bufferedReader.readLine()) != null) {
                sb.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            try {
                bufferedReader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        Log.e("TAG","下載txt文件");
        Log.e("TAG",sb.toString());
        return sb.toString();
    }

    /**
     * 讀取任何文件
     * 返回-1 ，代表下載失敗。返回0，代表成功。返回1代表文件已經存在
     *
     * @param urlStr
     * @param path
     * @param fileName
     * @return
     */
    public int downlaodFile(String urlStr, String path, String fileName) {
        InputStream input = null;


        try {
            FileUtil fileUtil = new FileUtil();
            if (fileUtil.isFileExist(path + fileName)) {
                return 1;
            } else {
                input = getInputStearmFormUrl(urlStr);
                File resultFile = fileUtil.write2SDFromInput(path,fileName,input);
                if (resultFile == null)
                    return -1;
            }
        } catch (IOException e) {
            e.printStackTrace();
            return -1;
        }
        finally {
            try {
                input.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return  0;
    }


    public InputStream getInputStearmFormUrl(String urlStr) throws IOException {
        url = new URL(urlStr);
        HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
        InputStream input = urlConn.getInputStream();
        return input;
    }
}

FileUtil.java

package util;

import android.os.Environment;

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

/**
 * Created by Spring on 2015/11/7.
 */
public class FileUtil {
    private String SDPATH;

    public FileUtil() {

    }

    public String getSDPATH() {
        return SDPATH;
    }

    public FileUtil(String SDPATH){
        //得到外部存儲設備的目錄（/SDCARD）
        SDPATH = Environment.getExternalStorageDirectory() + "/" ;
    }

    /**
     * 在SD卡上創建文件
     * @param fileName
     * @return
     * @throws java.io.IOException
     */
    public File createSDFile(String fileName) throws IOException {
        File file = new File(SDPATH + fileName);
        file.createNewFile();
        return file;
    }

    /**
     * 在SD卡上創建目錄
     * @param dirName 目錄名字
     * @return 文件目錄
     */
    public File createDir(String dirName){
        File dir = new File(SDPATH + dirName);
        dir.mkdir();
        return dir;
    }

    /**
     * 判斷文件是否存在
     * @param fileName
     * @return
     */
    public boolean isFileExist(String fileName){
        File file = new File(SDPATH + fileName);
        return file.exists();
    }

    public File write2SDFromInput(String path,String fileName,InputStream input){
        File file = null;
        OutputStream output = null;

        try {
            createDir(path);
            file =createSDFile(path + fileName);
            output = new FileOutputStream(file);
            byte [] buffer = new byte[4 * 1024];
            while(input.read(buffer) != -1){
                output.write(buffer);
                output.flush();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            try {
                output.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return file;
    }
}

3.MainActivity

package com.jingling.practice.downloadtest;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import util.HttpDownloader;


public class MainActivity extends Activity {
    HttpDownloader downloader ;

    private Button btn_downFile;
    private Button btn_downMP3;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn_downFile = (Button)this.findViewById(R.id.button);
        btn_downMP3 = (Button)this.findViewById(R.id.button2);
        btn_downFile.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloader = new HttpDownloader();
                String urlStr = "http://172.17.54.91:8080/download/down.txt";
                downloader.download(urlStr);
            }
        });
        btn_downMP3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String urlStr="http://172.17.54.91:8080/download/1.mp3";
                String path="file";
                String fileName="2.mp3";
                HttpDownloader httpDownloader = new HttpDownloader();
                httpDownloader.downlaodFile(urlStr,path,fileName);
            }
        });
    }



}

Android HTTP下載文件並保存到本地或SD卡