获取网络数据

1.URL地址

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

2.建立连接

HttpURLConnection urlConnection = (HttpURLConnection )url.openConnection;

3.连接成功判断

if(urlConnection .getResponseCode()==200)
{
  Log.i("test","连接成功");
}

4.开始传输数据获取相应的对象流

InputStream in = urlConnection .getInputStream()

5.如果操作成功，应关闭对象，关闭连接

urlConnection .disconnect()

完整例子

package com.example.dz.mygrame;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.annotation.Nullable;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

/**
 * Created by DZ on 2017/11/24.
 */


public class mymain extends Activity {
    private ImageView ivDown ;
    private Button btDown ;
    private int ERROR=2;
    private int i=0;
    private String [] str = {"https://gss0.bdstatic.com/7Po4cT78BgN3otqbppnN2DJv/baike/abpic/item/b8389b504fc2d56206e31a90e31190ef77c66ce0.jpg?k=img_47",
             "https://ss1.bdstatic.com/70cFuXSh_Q1YnxGkpoWK1HF6hhy/it/u=3036132189,30620540&fm=27&gp=0.jpg",
            "https://ss0.bdstatic.com/70cFvHSh_Q1YnxGkpoWK1HF6hhy/it/u=2346337118,3956192888&fm=27&gp=0.jpg",
    "https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=2827887652,1878401612&fm=27&gp=0.jpg"};
//图片地址
    private Handler handler = new Handler(){
//修改界面
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if(msg.what==1)
            {
                ivDown.setImageBitmap((Bitmap) msg.obj);
            }else if(msg.what==ERROR)
            {
                Toast.makeText(mymain.this,"失败",Toast.LENGTH_SHORT).show();
            }

          //  ivDown.setBackground((Drawable) msg.obj);
        }
    };
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.intern);

        ivDown = (ImageView) findViewById(R.id.iv_down);
        btDown = (Button) findViewById(R.id.btn_down);

        btDown.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                /*
                * 主线程中不允许访问网络
                * 访问网络需要加权限//
                *
                * */
                new mythread().start();
                i= ((i+1)%4);
            }
        });
    }
    private class  mythread extends Thread{
        @Override
        public void run() {
         /*   1.URL地址
            URL url = new URL ("http://www.baidu.com/");
            URL url = URL ("http://www.baidu.com/");
            2.建立连接
            HttpURLConnection urlConnection = (HttpURLConnection )url.openConnection;
            3.连接成功判断
            if(urlConnection .getResponseCode()==200)
            {
                Log.i("test","连接成功");
            }
            4.开始传输数据获取相应的对象流
            InputStream in = urlConnection .getInputStream()
            5.如果操作成功，应关闭对象，关闭连接
            urlConnection .disconnect()*/
            Log.i("test","子线程开始运行");
            Bitmap bitmap = null ;
            InputStream in = null;
            try {
                URL url = new URL (str[i]);
                HttpURLConnection conn = (HttpURLConnection)url.openConnection();
                if(conn.getResponseCode()==200){
                    Log.i("test","连接成功");
                     in = conn.getInputStream();
                    bitmap = BitmapFactory.decodeStream(in);
                   Message msg = new Message();
                    msg.obj = bitmap;
                    msg.what=1;
                    handler.sendMessage(msg);

                    /*byte[] bytes=new byte[1024];
                    in.read(bytes);
                    Log.i("test",String.valueOf(bytes));*/
                }
            } catch (Exception e) {
                e.printStackTrace();

                Message msg = new Message();
                msg.obj = bitmap;
                msg.what=ERROR;
                handler.sendMessage(msg);
            }finally {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}