廢話少說，直接上程式碼。簡單易懂。

xml如下：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_net"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation=
 
"vertical"
tools:context="com.example.waterlamp.NetActivity">
    <Button
android:id="@+id/okhttp"
android:text="okhttp請求"
android:layout_width="150dp"
android:layout_height="37dp"
android:layout_alignBottom="@+id/http"
android:layout_alignParentEnd="true"
android:layout_alignParentTop="true" />
 
    <Button
android:id="@+id/http"
android:text="HTTP請求"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_alignParentStart="true" />
    <ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
 
android:layout_alignParentStart="true"
android:layout_below="@+id/okhttp"
android:layout_alignParentBottom="true"
android:layout_alignParentEnd="true" >
        <TextView
android:id="@+id/stringData"
android:layout_width="match_parent"
android:layout_height="match_parent" />
    </ScrollView>
</RelativeLayout>

public class NetActivity extends AppCompatActivity implements View.OnClickListener{
private Button http,okhttp;
    private TextView stringData;
    private String web="https://www.baidu.com";
@Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
setContentView(R.layout.activity_net);
http= (Button) findViewById(R.id.http);
okhttp= (Button) findViewById(R.id.okhttp);
stringData= (TextView) findViewById(R.id.stringData);
http.setOnClickListener(this);
okhttp.setOnClickListener(this);
}

    @Override
public void onClick(View v) {
       switch (v.getId()){
           case R.id.http:
               sendRequestWithHttpURLConnection();
           break;
           case R.id.okhttp:
               sendRequestWithokHttp();
           break;
}
    }
    private void sendRequestWithHttpURLConnection(){
        new Thread(new Runnable() {
            @Override
public void run() {
                HttpURLConnection connection=null;
BufferedReader reader=null;
                try {
                    URL url=new URL(web);
connection= (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(5000);
connection.setReadTimeout(5000);
InputStream in=connection.getInputStream();
reader=new BufferedReader(new InputStreamReader(in));
StringBuffer response=new StringBuffer();
String line;
                    while ((line=reader.readLine())!=null){
                        response.append(line);
}
                    showRespond(response.toString());
} catch (MalformedURLException e) {
                    e.printStackTrace();
} catch (IOException e) {
                    e.printStackTrace();
}finally {
                    if (reader!=null){
                        try {
                            reader.close();
} catch (IOException e) {
                            e.printStackTrace();
}
                    }
                }
            }
        }).start();
}

    private void showRespond(final String response) {
        runOnUiThread(new Runnable() {
            @Override
public void run() {
                stringData.setText(response);
}
        });
}
    private void sendRequestWithokHttp(){
        new Thread(new Runnable() {
            @Override
public void run() {

                try {
                    OkHttpClient client=new OkHttpClient();
Request request=new Request.Builder()
                            .url(web).build();
Response  response=client.newCall(request).execute();
String str=response.body().string();
showRespond(str);
} catch (IOException e) {
                    e.printStackTrace();
}
            }
        }).start();
}
}

注意：需要在加許可權 

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

2.okhttp3需要在gradle新增依賴

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
})
    compile 'com.android.support:appcompat-v7:24.2.1'
compile 'com.android.support:design:24.2.1'
compile 'com.squareup.okhttp3:okhttp:3.4.1'//依賴testCompile 'junit:junit:4.12'
}