public class MainActivity extends AppCompatActivity { 26     private final int POST_VALUE = http://www.mamicode.com/1; 42     String text ="";
    //这里不能获取ID，因为下面还没连接到activity_main,xml
    TextView textView;
    //--------------------------------------------定义一个Handler来处理消息----------------------------------------------
    final Handler handler = new Handler() {
        @Override
        public void handleMessage(Message message) {
            switch (message.what) { 54                 case POST_VALUE:
                    textView.setText(text = (text + "=" + message.obj));
                    text = "";
                    break;103                 default:
                    break;
            }
        }
    };
    //-----------------------------------------------------------------------------------------------------
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = (TextView) findViewById(R.id.textView);131        
　 //-------------------------------------------设置符号=的监听--------------------------------------------------
        Button sendGET = (Button) findViewById(R.id.send);
        sendGET.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {152                     new Thread(new Runnable() {
                        @Override
                        public void run() {
                            if(strTmp.length==2){
                                CalBean tb = new CalBean(10, 2, plus);
                                Gson gson = new Gson();
                                //传入的参数
                                String datas = gson.toJson(tb);
                                String url = "http://100.108.129.56:8080/example/cal";
                                String data = sendPostRequest(url, datas);
                                Message message = new Message();
                                message.what = POST_VALUE;
                                message.obj = data.toString();
                                handler.sendMessage(message);
                            }
                        }
                    }).start();
                } catch (Exception e) {
                    Log.i("ok", "there must be something wrong!");
                    return;
                }
            }
        });
        //----------------------------------------------------------------------------------------------------- 
    }
    public static String sendPostRequest(String url, String param) {
        HttpURLConnection httpURLConnection = null;
        OutputStream out = null; //写
        InputStream in = null;   //读
        int responseCode = 0;    //远程主机响应的HTTP状态码
        String result = "";
        try {
            URL sendUrl = new URL(url);
            httpURLConnection = (HttpURLConnection) sendUrl.openConnection();
            //post方式请求
            httpURLConnection.setRequestMethod("POST");
            //设置头部信息
            httpURLConnection.setRequestProperty("headerdata", "ceshiyongde");
            //一定要设置 Content-Type 要不然服务端接收不到参数
            httpURLConnection.setRequestProperty("Content-Type", "application/Json; charset=UTF-8");
            //指示应用程序要将数据写入URL连接,其值默认为false（是否传参）
            httpURLConnection.setDoOutput(true);
            //httpURLConnection.setDoInput(true);
            httpURLConnection.setUseCaches(false);
            httpURLConnection.setConnectTimeout(30000); //30秒连接超时
            httpURLConnection.setReadTimeout(30000);    //30秒读取超时
            //传入参数
            out = httpURLConnection.getOutputStream();
            out.write(param.getBytes());
            out.flush(); //清空缓冲区,发送数据
            out.close();
            responseCode = httpURLConnection.getResponseCode();
            //获取请求的资源
            BufferedReader br = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream(), "UTF-8"));
            result = br.readLine();
        } catch (Exception e) {
            e.printStackTrace();
        }
        Map<String, String> map = new Gson().fromJson(result,
                new TypeToken<Map<String, String>>() {
                }.getType());
        return map.get("result");
    }
}

public class CalBean {
    private float para1;
    private float para2;
    private String opt;

    public CalBean(float para1, float para2, String opt) {
        this.para1 = para1;
        this.para2 = para2;
        this.opt = opt;
    }

    public CalBean(){};

    public float getpara1() {
        return para1;
    }

    public float getPara2() {
        return para2;
    }

    public String getOpt() {
        return opt;
    }

    public void setpara1(float para1) {
        this.para1 = para1;
    }

    public void setPara2(float para2) {
        this.para2 = para2;
    }

    public void setOpt(String opt) {
        this.opt = opt;
    }

    @Override
    public String toString() {
        return "CalBean{" +
                "para1=" + para1 +
                ", para2=" + para2 +
                ", opt=‘" + opt + ‘\‘‘ +
                ‘}‘;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:rowCount="7"
    android:columnCount="4"
    tools:context="com.example.weihy.fourfour.MainActivity"
    >

    <TextView
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:id="@+id/textView"
        android:layout_columnSpan="4"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="="
        android:id="@+id/send"
        />
</GridLayout>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.weihy.fourfour">
    <uses-permission android:name="android.permission.INTERNET"/>
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>