使用HTTP协议访问网络

1 HttpURLConnection
2 HttpClient

HttpURLConnection使用过程：
1 获取HttpURLConnection的实例：
URL url = new URL（“http://www.baidu.com”）；
HttpURLConnection connection = （HttpURLConnection）url.openConnection;
2 设置请求的方法：GET POST 获取/提交
connection.setRequsestMethod(“get”);
3 自由设置
connection.setConnectionTimeout(8000);
connection.setReadTimeout(8000);
4 获取服务器返回的输入流
InputStream in = connection.getInputStream（）；
5 最后调用connection.disconnect();

实例：get

<?xml version="1.0" encoding="utf-8"?><LinearLayout 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"    android:orientation="vertical"    >    <Button        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:id="@+id/send_request"        android:text="Send Request"/>    <ScrollView        android:layout_width="match_parent"        android:layout_height="match_parent">        <TextView            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:id="@+id/response_text"/>    </ScrollView></LinearLayout>

package com.example.networktest;import android.os.Handler;import android.os.Message;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import java.io.BufferedReader;import java.io.InputStream;import java.io.InputStreamReader;import java.net.HttpURLConnection;import java.net.URL;public class MainActivity extends AppCompatActivity implements View.OnClickListener {    public static  final  int SHOW_RESPONSE = 0;    private Button sendRquest;    private TextView responseText;    private Handler handler = new Handler(){        @Override        public void handleMessage(Message msg) {           switch (msg.what) {               case SHOW_RESPONSE:                   String response = (String) msg.obj;                   //进行UI操作                   responseText.setText(response);           }        }    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        sendRquest = (Button) findViewById(R.id.send_request);        responseText = (TextView) findViewById(R.id.response_text);        sendRquest.setOnClickListener(this);    }    @Override    public void onClick(View v) {        if(v.getId() == R.id.send_request){            sendRequestWithHttpURLConnection();        }    }    private  void sendRequestWithHttpURLConnection(){        //开启线程        new Thread(new Runnable() {            @Override            public void run() {                HttpURLConnection connection = null;                try {                    URL url = new URL("http://www.baidu.com");                    connection = (HttpURLConnection) url.openConnection();                    connection.setRequestMethod("GET");                    connection.setConnectTimeout(8000);                    connection.setReadTimeout(8000);                    InputStream in = connection.getInputStream();                    BufferedReader reader = new BufferedReader((new InputStreamReader(in)));                    StringBuilder response = new StringBuilder();                    String line ;                    while ((line = reader.readLine())!= null){                        response.append(line);                    }                    Message message = new Message() ;                    message.what = SHOW_RESPONSE ;                    message.obj = response.toString();                    handler.sendMessage(message);                }catch (Exception e){                    e.printStackTrace();                }finally {                    if (connection!=null){                        connection.disconnect();                    }                }            }        }).start();    }}

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

post

public static String loginOfPost(String username, String password) {                HttpURLConnection conn = null;                try {                        // 创建一个URL对象                        URL mURL = new URL("http://192.168.0.100:8080/android/servlet/LoginServlet");                        // 调用URL的openConnection()方法,获取HttpURLConnection对象                        conn = (HttpURLConnection) mURL.openConnection();                        conn.setRequestMethod("POST");// 设置请求方法为post                        conn.setReadTimeout(5000);// 设置读取超时为5秒                        conn.setConnectTimeout(10000);// 设置连接网络超时为10秒                        conn.setDoOutput(true);// 设置此方法,允许向服务器输出内容                        // post请求的参数                        String data = "username=" + username + "&password=" + password;                        // 获得一个输出流,向服务器写数据,默认情况下,系统不允许向服务器输出内容                        OutputStream out = conn.getOutputStream();// 获得一个输出流,向服务器写数据                        out.write(data.getBytes());                        out.flush(); // 刷新对象输出流，将任何字节都写入潜在的流中                        out.close();                        int responseCode = conn.getResponseCode();// 调用此方法就不必再使用conn.connect()方法                        if (responseCode == 200) {                                InputStream is = conn.getInputStream();                                String state = getStringFromInputStream(is);                                return state;                        } else {                                Log.i(TAG, "访问失败" + responseCode);                        }                } catch (Exception e) {                        e.printStackTrace();                } finally {                        if (conn != null) {                                conn.disconnect();// 关闭连接                        }                }                return null;        }

2 使用HttpClient （在Android 6.0（API 23） 中，Google已经移除了Apache HttpClient 想关类，推荐使用HttpUrlConnection，如果要继续使用，在Android studio对应的module下的build.gradle文件中加入：
android {
useLibrary ‘org.apache.http.legacy’
}）

package com.example.networktest;import android.net.Uri;import android.os.Handler;import android.os.Message;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import com.google.android.gms.appindexing.Action;import com.google.android.gms.appindexing.AppIndex;import com.google.android.gms.common.api.GoogleApiClient;import org.apache.http.HttpEntity;import org.apache.http.HttpResponse;import org.apache.http.client.HttpClient;import org.apache.http.client.methods.HttpGet;import org.apache.http.impl.client.DefaultHttpClient;import org.apache.http.util.EntityUtils;import java.io.BufferedReader;import java.io.InputStream;import java.io.InputStreamReader;import java.net.HttpURLConnection;import java.net.URL;public class MainActivity extends AppCompatActivity implements View.OnClickListener {    public static final int SHOW_RESPONSE = 0;    private Button sendRquest;    private TextView responseText;    private Handler handler = new Handler() {        @Override        public void handleMessage(Message msg) {            switch (msg.what) {                case SHOW_RESPONSE:                    String response = (String) msg.obj;                    //进行UI操作                    responseText.setText(response);            }        }    };    /**     * ATTENTION: This was auto-generated to implement the App Indexing API.     * See https://g.co/AppIndexing/AndroidStudio for more information.     */    private GoogleApiClient client;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        sendRquest = (Button) findViewById(R.id.send_request);        responseText = (TextView) findViewById(R.id.response_text);        sendRquest.setOnClickListener(this);        // ATTENTION: This was auto-generated to implement the App Indexing API.        // See https://g.co/AppIndexing/AndroidStudio for more information.        client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();    }    @Override    public void onClick(View v) {        if (v.getId() == R.id.send_request) {            // sendRequestWithHttpURLConnection();            sendRequestWithHttpClient();        }    }    private void sendRequestWithHttpURLConnection() {        //开启线程        new Thread(new Runnable() {            @Override            public void run() {                HttpURLConnection connection = null;                try {                    URL url = new URL("http://www.baidu.com");                    connection = (HttpURLConnection) url.openConnection();                    connection.setRequestMethod("GET");                    connection.setConnectTimeout(8000);                    connection.setReadTimeout(8000);                    InputStream in = connection.getInputStream();                    BufferedReader reader = new BufferedReader((new InputStreamReader(in)));                    StringBuilder response = new StringBuilder();                    String line;                    while ((line = reader.readLine()) != null) {                        response.append(line);                    }                    Message message = new Message();                    message.what = SHOW_RESPONSE;                    message.obj = response.toString();                    handler.sendMessage(message);                } catch (Exception e) {                    e.printStackTrace();                } finally {                    if (connection != null) {                        connection.disconnect();                    }                }            }        }).start();    }    private void sendRequestWithHttpClient() {        new Thread(new Runnable() {            @Override            public void run() {                try {                    HttpClient httpClient = new DefaultHttpClient();                    HttpGet httpGet = new HttpGet("http://www.baidu.com");                    HttpResponse httpResponse = httpClient.execute(httpGet);                    if (httpResponse.getStatusLine().getStatusCode() == 200){                        HttpEntity entity =httpResponse.getEntity();                        String response = EntityUtils.toString(entity,"utf-8");                        Message message = new Message();                        message.what = SHOW_RESPONSE ;                        message.obj = response.toString();                        handler.sendMessage(message);                    }                } catch (Exception e) {                    e.printStackTrace();                }            }        }).start();    }    @Override    public void onStart() {        super.onStart();        // ATTENTION: This was auto-generated to implement the App Indexing API.        // See https://g.co/AppIndexing/AndroidStudio for more information.        client.connect();        Action viewAction = Action.newAction(                Action.TYPE_VIEW, // TODO: choose an action type.                "Main Page", // TODO: Define a title for the content shown.                // TODO: If you have web page content that matches this app activity's content,                // make sure this auto-generated web page URL is correct.                // Otherwise, set the URL to null.                Uri.parse("http://host/path"),                // TODO: Make sure this auto-generated app URL is correct.                Uri.parse("android-app://com.example.networktest/http/host/path")        );        AppIndex.AppIndexApi.start(client, viewAction);    }    @Override    public void onStop() {        super.onStop();        // ATTENTION: This was auto-generated to implement the App Indexing API.        // See https://g.co/AppIndexing/AndroidStudio for more information.        Action viewAction = Action.newAction(                Action.TYPE_VIEW, // TODO: choose an action type.                "Main Page", // TODO: Define a title for the content shown.                // TODO: If you have web page content that matches this app activity's content,                // make sure this auto-generated web page URL is correct.                // Otherwise, set the URL to null.                Uri.parse("http://host/path"),                // TODO: Make sure this auto-generated app URL is correct.                Uri.parse("android-app://com.example.networktest/http/host/path")        );        AppIndex.AppIndexApi.end(client, viewAction);        client.disconnect();    }}