Android入门教程 HttpURLConnection的用法 HTTP请求

写在前面：
android使用网络一定记得加上网络访问权限

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

一、使用HttpURLConnection发送网络请求

1、get方式发送请求

step1:创建URL对象
step2:通过URL对象调用openConnection()方法获得HttpURLConnection对象
step3:HttpURLConnection对象设置其他连接属性
step4:HttpURLConnection对象调用getInputStream()方法向服务器发送http请求 并获取到服务器返回的输入流
step5:读取输入流，转换成String字符串

注意：
网络请求，通常耗时较长，所以不能在主线程中进行，需要单独开一个子线程进行网络请求

代码示例

public class MainActivity extends Activity {    private TextView webTextView;    private String webText;    private Handler mHandler = new Handler(){        public void handleMessage(android.os.Message msg) {            if(msg.what==1){                webTextView.setText(webText);            }        };    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        webTextView = (TextView) findViewById(R.id.web_text);        //创建线程对象        MyThread mThread = new MyThread();        //启动线程        new Thread(mThread).start();    }    /**     * 定义一个子线程，在子线程中访问网络     * @author jiangjunjie     *     */    private class MyThread implements Runnable{        @Override        public void run() {            try {                URL url = new URL("http://www.baidu.com");                HttpURLConnection mConnection = (HttpURLConnection) url.openConnection();                mConnection.setConnectTimeout(10000);//设置连接超时                //创建输入流                InputStream in = null;                //判断连接返回码                if(mConnection.getResponseCode()==200){                    //返回码是200时，表明连接成功                    in = mConnection.getInputStream();                }                //创建输入流读取对象                InputStreamReader inReader = new InputStreamReader(in, "UTF-8");                //输入流缓存读取                BufferedReader bufferedReader = new BufferedReader(inReader);                StringBuffer sb = new StringBuffer();                String temp = null;                //输入流转换成String                while((temp=bufferedReader.readLine())!=null){                    sb.append(temp);                }                webText = sb.toString();            } catch (IOException e) {                e.printStackTrace();            }            //Handler创建消息对象            Message msg = mHandler.obtainMessage();            msg.what = 1;            //发送Handler消息            mHandler.sendMessage(msg);        }    }}

2、post方式发送请求

post请求方式和get方式步骤类似，只需添加一句

mConnection.setRequestMethod("POST");

二、使用HttpURLConnection加载网络图片

加载网络图片，需要用到Bitmap对象。
加载网络图片有时也需耗时较长时间，所以也应该异步加载。
在此，以AsyncTask为例。

效果图

ShowWebPicActivity代码示例

public class ShowWebPicActivity extends Activity {    Button showBtn;    ImageView webimgView;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_show_web_pic);        bindID();        showBtn.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                DownloadImgTask task = new DownloadImgTask(ShowWebPicActivity.this, showBtn, webimgView);                task.execute("http://img31.mtime.cn/mg/2012/10/30/201631.37192876.jpg");            }        });    }    private void bindID() {        showBtn = (Button) findViewById(R.id.show_btn);        webimgView = (ImageView) findViewById(R.id.pic_img);    }}

DownloadImgTask代码

public class DownloadImgTask extends AsyncTask<String, Integer, Integer>{    private Context context;    private Button btn;    private ImageView imageView;    //加载网络图片需要用到Bitmap对象    private Bitmap bitmap;    public DownloadImgTask(Context context,Button btn,ImageView imgview) {        this.context = context;        this.btn = btn;        this.imageView = imgview;    }    @Override    protected Integer doInBackground(String... params) {        try {            //创建URL对象            URL url = new URL(params[0]);            //通过URL对象得到HttpURLConnection            HttpURLConnection connection = (HttpURLConnection) url.openConnection();            //得到输入流            InputStream inputStream = connection.getInputStream();            bitmap = BitmapFactory.decodeStream(inputStream);        } catch (MalformedURLException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }        return 1;    }    @Override    protected void onPostExecute(Integer result) {        super.onPostExecute(result);        switch (result) {        case 1:            imageView.setImageBitmap(bitmap);            break;        default:            break;        }    }}

三、使用HttpURLConnection下载网络资源

下载网络资源用到的知识点，除了网络资源访问，还需要用到文件操作的知识，比如判断文件是否存在、创建目录、创建文件等等。

activity_download.xml布局文件代码

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context="${relativePackage}.${activityClass}" >    <ProgressBar         android:layout_width="match_parent"        android:layout_height="wrap_content"        android:id="@+id/progressbar"        style="?android:attr/progressBarStyleHorizontal"        />    <Button         android:layout_width="match_parent"        android:layout_height="wrap_content"        android:text="下载"        android:id="@+id/downloadBtn"        android:layout_below="@id/progressbar"        /></RelativeLayout>

DownloadActivity代码

public class DownloadActivity extends Activity {    ProgressBar progressBar;    Button downloadBtn;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_download);        bindID();        downloadBtn.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                downloadBtn.setEnabled(false);                //构造方法初始化                DownLoadTask dTask = new DownLoadTask(DownloadActivity.this,downloadBtn,progressBar);                //执行任务                dTask.execute("http://img1.bitautoimg.com/bitauto/2012/09/17/a50cdcf8-1a2a-418b-b7be-d81f36ab12ee.jpg","fra.jpg");            }        });    }    private void bindID() {        progressBar = (ProgressBar) findViewById(R.id.progressbar);        downloadBtn = (Button) findViewById(R.id.downloadBtn);    }}

DownLoadTask代码

public class DownLoadTask extends AsyncTask<String, Integer, Integer> {    private Context context;    private Button btn;    private ProgressBar pBar;    private String SDPATH = "";    private String PATH="";    /**     * 构造方法     * @param context Activity上下文环境     * @param btn   下载按钮     * @param pBar  进度条     */    public DownLoadTask(Context context,Button btn,ProgressBar pBar) {        this.context = context;        this.btn = btn;        this.pBar = pBar;        this.SDPATH = Environment.getExternalStorageDirectory() + "/";        this.PATH = this.SDPATH+"download_pic/";        System.out.println("PATH***:"+PATH);    }    @Override    protected Integer doInBackground(String... params) {        //定义输入流和输出流对象        InputStream inputStream = null;        OutputStream outputStream = null;        //定义文件对象        File file = null;        //判断文件是否存在        if (isFileExists(PATH+params[1])) {            //如果存在，直接返回，执行onPostExecute方法            return 1;        }        try {            //创建URL对象            URL url = new URL(params[0]);            //通过URL对象创建HTTP连接            HttpURLConnection httpUrlConnection = (HttpURLConnection) url.openConnection();            //判断返回码            if (httpUrlConnection.getResponseCode() == 200) {                inputStream = httpUrlConnection.getInputStream();                // 更新进度条(设置进度条总长度)                publishProgress(-2, httpUrlConnection.getContentLength());            } else {                // 下载有误，网络连接错误                publishProgress(-1);            }            //创建目录            createDir(PATH);            //创建文件            file = createFile(PATH+params[1]);            //创建输出流            outputStream = new FileOutputStream(file);            //创建缓冲区            byte buffer[] = new byte[4*1024];            int length = 0;            int sum = 0;            while((length = inputStream.read(buffer))!=-1){                outputStream.write(buffer,0,length);                //已经下载的长度                sum+=length;                //更新进度条                publishProgress(0,sum);            }            outputStream.flush();//强制把缓冲区的数据写入到文件并清空缓冲区        } catch (IOException e) {            e.printStackTrace();        }        return 0;    }    /**     * 下载过程中执行此方法     * @param values     */    @Override    protected void onProgressUpdate(Integer... values) {        super.onProgressUpdate(values);        switch (values[0]) {        case 0:            pBar.setProgress(values[1]);            break;        case -1:            Toast.makeText(context, "网络连接错误，请检查下载链接是否正确", Toast.LENGTH_LONG).show();            break;        case -2:            pBar.setMax(values[1]);            break;        default:            break;        }    }    /**     * 下载完成后执行此方法     * @param result     */    @Override    protected void onPostExecute(Integer result) {        super.onPostExecute(result);        btn.setEnabled(true);        switch (result) {        case 1:            Toast.makeText(context, "文件已存在", Toast.LENGTH_LONG).show();            break;        default:            break;        }    }    /**     * 工具方法——判断文件已存在     *      * @return     */    private boolean isFileExists(String fileName) {        File file = new File(fileName);        if (file.exists()) {            // 文件已存在            return true;        }        return false;    }    /**     * 工具方法——创建目录     */    private boolean createDir(String dirName) {        File file = new File(dirName);        boolean isCreateDir = file.mkdir();        return isCreateDir;    }    /**     * 工具方法——创建文件     * @param string     */    private File createFile(String fileName) {        File file = new File(fileName);        boolean isCreateFile  = false;        try {            isCreateFile = file.createNewFile();        } catch (IOException e) {            e.printStackTrace();        }        return file;    }}