<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"
    tools:context="com.zzw.watctImage.MainActivity" >

    <ImageView
        android:id="@+id/image_view"
        android:layout_width="match_parent"
        android:src="@drawable/t01a7b264978bb316f1"
        android:layout_height="wrap_content"
        android:layout_weight="1" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal" >

        <EditText
            android:id="@+id/url_edit"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:singleLine="true"
            android:text="http://p1.so.qhimg.com/t017cf2863df563308b.jpg" />

        <Button
            android:id="@+id/get"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:text="獲得圖片"
            android:textColor="@android:color/holo_blue_light" />
    </LinearLayout>

</LinearLayout>

XML
 

package com.zzw.watctImage;

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

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;

public class MainActivity extends Activity implements OnClickListener {
    ImageView image_view = null;
    EditText image_uri = null;
    Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            // TODO Auto-generated method stub
            super.handleMessage(msg);
            if (msg.what == 0) {
                Bitmap bitmap = (Bitmap) msg.obj;
                image_view.setImageBitmap(bitmap);
            }

        }

    };
    /**
     * 1.訪問網路不能直接放在主方法裡面（android.os.NetworkOnMainThreadException）, 應該放在一個執行緒裡面
     * 2.android.view.ViewRootImpl$CalledFromWrongThreadException:
     * 只能在主執行緒或者UI執行緒裡面修改檢視,應該用通訊來解決
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
    }

    // 初始化
    public void init() {
        image_view = (ImageView) findViewById(R.id.image_view);
        image_uri = (EditText) findViewById(R.id.url_edit);
        findViewById(R.id.get).setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        final String uri = image_uri.getText().toString();
        new Thread(new Runnable() {
            @Override
            public void run() {
                // TODO Auto-generated method stub
                Bitmap bitmap = getBitmap(uri);
                if (bitmap != null) {
                    Message msg = new Message();
                    msg.what = 0;// 說明你是誰
                    msg.obj = bitmap;
                    handler.sendMessage(msg);
                }

            }
        }).start();
        ;
    }

    // bitmap------>點陣圖
    public Bitmap getBitmap(String uri) {
        HttpURLConnection conn = null;
        try {
            // 1、獲得圖片的url
            URL url = new URL(uri);

            // 2、獲得網路連線
            conn = (HttpURLConnection) url.openConnection();

            // 3、設定請求的一些常用引數
            conn.setReadTimeout(3000);// 設定連線去讀取資料的最長時間
            conn.setConnectTimeout(3000);// 設定超時
            conn.setDoInput(true);// 設定請求可以讓伺服器寫入資料

            // 4、真正的請求圖片，然後把從伺服器上請求的二進位制流儲存到inputStream裡面
            conn.connect();
            InputStream in = conn.getInputStream();
            Bitmap bitmap = BitmapFactory.decodeStream(in);
            return bitmap;
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        // 5、關閉網路連線
        finally {
            if (conn != null) {
                conn.disconnect();
            }
        }
        return null;
    }
}

JAVA