HttpURLConnection基本使用

2019-08-20 本文已影响0人者文_

1. HttpURLConnection基本使用

HttpURLConnection是网络请求的基本类，在具体了解HttpURLConnection的基本使用前，先了解一些RUL

1.1 URL介绍

统一资源定位符URL（Uniform Resource Locator）是www客户机访问Internet时用来标识资源的名字和地址。

URL的基本格式是：

<METHOD>://<HOSTNAME:PORT>/<PATH>/<FILE>

Method是传输协议
HOSTNAME是文档和服务器所在的Internet主机名（域名系统中DNS中的点地址）
PORT是服务端口号（可省略）
PATH是路径名
FILE是文件名

示例：

http://www.weixueyuan.net/view/6079.html （www.weixueyuan.net是主机名，view/6079.html是文件路径和文件名）

简单的可以把URL理解为包含：协议、主机名、端口、路径、查询字符串和参数等内容。每一段可以独立设置。

Java中有个java.net包，其中的类是进行网络编程的，URL对象则是一个可以表示网络资源的类。程序利用URL对象能够实现Internet寻址、网络资源的定位连接、在客户机与服务器之间访问等。

URL对象的方法也很简单，基本上都是get方法，主要用于分段获取一个URL中各个部分，比单纯地使用一个字符串来表示链接地址，URL对象的方式更加灵活方便。

同时，它可以使用openConnection方法，获取一个URLConnection对象，以建立网络连接。

1.2 HttpURLConnection使用

HttpURLConnection的基本使用步骤如下：

获取HttpURLConnection实例，需new一个URL对象，传入目标网络地址

URL url = new URL("http://www.baidu.com);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();

设置HTTP请求使用方法：一般有两种：GET与POST
```
connection.setRequestMethod("GET");
```

自由定制，比如设置连接超时，读取超时毫秒数等

connection.setConnectionTimeout(8000);
connection.setReadTimeout(8000);

调用getInputStream()方法获取到服务器返回的输入流，对输入流进行读取
```
InputStream in = connection.getInputStream();
```
最后，调用disconnection()方法将这个HTTP连接关闭掉
```
connection.disconnection();
```

示例：

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    TextView responseText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button sendRequest = (Button) findViewById(R.id.send_request);
        responseText = (TextView) findViewById(R.id.response_text);
        sendRequest.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.send_request) {
            Log.e("MainActivity","first");
            sendRequestWithHttpURLConnection();
        }
    }

    private void sendRequestWithHttpURLConnection() {
        //开启线程发起网络请求
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection connection = null;
                BufferedReader reader = null;
                try {
                    //获取HttpRULConnection实例
                    URL url = new URL("https://www.baidu.com");
                    connection = (HttpURLConnection) url.openConnection();
                    //设置请求方法和自由定制
                    connection.setRequestMethod("GET");
                    connection.setConnectTimeout(8000);
                    connection.setReadTimeout(8000);
                    //获取响应码和返回的输入流
                    int i = connection.getResponseCode();
                    InputStream in = connection.getInputStream();
                    //对输入流进行读取
                    reader = new BufferedReader(new InputStreamReader(in));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null) {
                        response.append(line);
                    }
                    showResponse(response.toString());
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    if (reader != null) {
                        try {
                            reader.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                    if (connection != null) {
                        connection.disconnect();
                    }
                }
            }
        }).start();
    }

    private void showResponse( final String response) {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                //进行UI操作
                responseText.setText(response);
            }
        });
    }
}

在AndroidManifest.xml中注册权限

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

备注：（Android 9.0不能明文连接，需用https）

示例2：从网络中下载图片

修改activity_main.xml文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <Button
        android:id="@+id/send_request"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Send Request"/>
    <Button
        android:id="@+id/download_picture"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Download_picture"/>
    <ImageView
        android:id="@+id/imagPic"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <TextView
            android:id="@+id/response_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    </ScrollView>

</LinearLayout>

新建StreamTool.java文件，读取流中文件

public class StreamTool {
    //从流中读取数据
    public static byte[] read(InputStream inStream) throws Exception{
        ByteArrayOutputStream outStream = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int len = 0;
        while((len = inStream.read(buffer)) != -1)
        {
            outStream.write(buffer,0,len);
        }
        inStream.close();
        return outStream.toByteArray();
    }
}

新建GetData.java文件,获取数据类

public class GetData {
    // 定义一个获取网络图片数据的方法:
    public static byte[] getImage(String path) throws Exception {
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        // 设置连接超时为5秒
        conn.setConnectTimeout(5000);
        // 设置请求类型为Get类型
        conn.setRequestMethod("GET");
        // 判断请求Url是否成功
        if (conn.getResponseCode() != 200) {
            throw new RuntimeException("请求url失败");
        }
        InputStream inStream = conn.getInputStream();
        byte[] bt = StreamTool.read(inStream);
        inStream.close();
        return bt;
    }
}

修改MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private TextView responseText;
    private String picture = "https://i.ytimg.com/vi/ck-2nnFC8oE/hqdefault.jpg";
    private Bitmap bitmap;
    private ImageView imgPic;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button sendRequest = (Button) findViewById(R.id.send_request);
        responseText = (TextView) findViewById(R.id.response_text);
        imgPic = (ImageView) findViewById(R.id.imagPic);
        Button downloadPicture = (Button) findViewById(R.id.download_picture);
        downloadPicture.setOnClickListener(this);
        sendRequest.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.send_request) {
            sendRequestWithHttpURLConnection();
        } else if (v.getId() == R.id.download_picture) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        byte[] data = GetData.getImage(picture);
                        bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);
                        showBitmap();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }).start();

        }
    }

    private void sendRequestWithHttpURLConnection() {
        //开启线程发起网络请求
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection connection = null;
                BufferedReader reader = null;
                try {
                    URL url = new URL("https://www.baidu.com");
                    connection = (HttpURLConnection) url.openConnection();
                    connection.setRequestMethod("GET");
                    connection.setConnectTimeout(8000);
                    connection.setReadTimeout(8000);
                    int i = connection.getResponseCode();
                    InputStream in = connection.getInputStream();
                    //对输入流进行读取
                    reader = new BufferedReader(new InputStreamReader(in));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null) {
                        response.append(line);
                    }
                    showResponse(response.toString());
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    if (reader != null) {
                        try {
                            reader.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                    if (connection != null) {
                        connection.disconnect();
                    }
                }
            }
        }).start();
    }

    private void showResponse( final String response) {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                //进行UI操作
                responseText.setText(response);
            }
        });
    }

    private void showBitmap() {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                imgPic.setImageBitmap(bitmap);
            }
        });
    }
}

备注：

HttpURLConnection的connect()函数，实际上只是建立了一个与服务器的tcp连接，并没有实际发送http请求。无论是post还是get，http请求实际上直到HttpURLConnection的getInputStream()这个函数里面才正式发送出去。

HttpURLConnection基本使用

1. HttpURLConnection基本使用

1.1 URL介绍

1.2 HttpURLConnection使用

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