分主线程，子线程，访问是否连接网络

import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.AsyncTask;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import com.example.asynctaskdemo.bean.Info;
import com.example.asynctaskdemo.utils.NetWorkUtils;
import com.example.asynctaskdemo.utils.StreamTools;
import com.google.gson.Gson;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

import java.net.URLEncoder;

public class MainActivity extends AppCompatActivity {

    public static final String TAG = "MainActivity";
    private ProgressDialog dialog;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        //new Thread + Handler  用异步任务类去替换
    }

    public void btnRequest(View v){
        //isConnection 返回的true，证明网络是连接的
        if(NetWorkUtils.isConnection(this)) {
            //有网就去请求数据
            getData();
        }else{
            //弹出一个对话框
            showNetWorkSettingDialog();
        }
    }
    /**
     * 使用异步任务执行网络请求
     * */
    private void getData(){
        //parameter : 放置请求连接地址以及请求参数 类型
        //Progress : 进度，当你们下载文件的时候，Integer
        //result: 限定你所请求网络数据返回的类型是什么,String
        new AsyncTask<String,Void,String>(){
            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                //就是准备加载时会执行
                //适合显示数据请求的加载框
                Log.e(TAG, "onPreExecute执行了" );

                showLoadDialog();

            }

            @Override
            protected void onPostExecute(String s) {
                super.onPostExecute(s);
                //当网络数据请求完毕时会被执行
                //这个方法是运行在主线程的，做UI的更新

                if(s != null){
                    //JSON  去解析json
                    Gson gson = new Gson();
                    Info info = gson.fromJson(s, Info.class);
                    //设置适配器
                    //lv.setAdapter();
                }

                //隐藏进度加载对话框
                dialog.dismiss();

            }

            @Override
            protected void onProgressUpdate(Void... values) {
                super.onProgressUpdate(values);
                //当今都更新的时候会被执行
                Log.e(TAG, "onProgressUpdate执行了 " );

            }

            @Override
            protected String doInBackground(String... params) {
                try {
                    //耗时操作都在这里执行,子线程
                    //String...大家可以可变参数类型看作是一个数组

                    String path = params[0];
                    URL url = new URL(path);
                    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                    connection.setRequestMethod("GET");
                    connection.setConnectTimeout(5*1000);
                    connection.setReadTimeout(5*1000);
                    int code = connection.getResponseCode();

                    if(code == HttpURLConnection.HTTP_OK){//判断服务是否成功应答
                        //服务成功应答
                        InputStream is = connection.getInputStream();
                        String json = StreamTools.readFromNetWork(is);
                        return json;
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
                return null;
            }
        }.execute("http://apis.juhe.cn/cook/query.php?key=ff00d7339861c7fd7d5b54b16b76422a&menu="+ URLEncoder.encode("黄焖鸡"));
    }
    /**
     * 展示一个加载进度对话框
     */
    private void showLoadDialog(){
        dialog = new ProgressDialog(this);
        dialog.setMessage("顾晓彬玩命加载中...");
        dialog.show();
    }
    /**
     * 设置网络设置提示对话框
     */
    private void showNetWorkSettingDialog(){

        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setMessage("没有设置网络，请您设置网络!");
        builder.setNegativeButton("取消",null);
        builder.setPositiveButton("设置", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                //跳转网络设置界面  隐士意图
                Intent intent = new Intent();
                intent.setAction("android.settings.WIRELESS_SETTINGS");
                startActivity(intent);
            }
        });

        builder.create().show();

    }

//第二个类被调用用
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;

/**
 * 网络判断的工具类
 */

public class NetWorkUtils {


    /**
     * 检查设备网络是否连接
     * @return
     */
    public static boolean isConnection(Context context){

        //得到管理网络的服务实例
        ConnectivityManager connMgr = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);
        //得到网络信息 (判断网络是否连接、3G、4G)
        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
        //判断网络是否已经连接，如果连接的话，返回true，否则false
        return (networkInfo != null && networkInfo.isConnected());

    }

必须加权限

ACCESS_NETWORK_STATE