public class MainActivity extends AppCompatActivity {
    private Button button;
    private  File file;
    private  String path;
    private Handler handler=new Handler(){
        @Override
public void handleMessage(Message msg) {
            switch (msg.what){
                case 0:
                    ImageView iv= (ImageView) findViewById(R.id.imageView
 
);
                    iv.setImageBitmap((Bitmap) msg.obj);
                    Toast.makeText(MainActivity.this,"從網路獲取圖片",Toast.LENGTH_LONG).show();
                    break;
                case 1:
                    Toast.makeText(MainActivity.this,"獲取圖片失敗",Toast.LENGTH_LONG).show();
                    break
 
;
            }
        }
    };

    @Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
         button= (Button) findViewById(R.id.button);


    }
    public void click(View view) {
         path 
 
= "http://192.168.3.2:8080/hehe.jpg";
        file = new File(getCacheDir(), getFileName(path));
        if (file.exists()) {
            Bitmap bm= BitmapFactory.decodeFile(file.getAbsolutePath());
            ImageView iv= (ImageView) findViewById(R.id.imageView);
            iv.setImageBitmap(bm);
            Toast.makeText(MainActivity.this,"快取的圖片",Toast.LENGTH_LONG).show();
        }
        else {
            new Thread() {
                @Override
public void run() {
                    //設定網路路徑
//設定URL
try {
                        URL url = new URL(path);
                        //獲取網路連線物件
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                        //初設連線設定,請求方式，讀取超時，連線超時
conn.setRequestMethod("GET");
                        conn.setReadTimeout(5000);
                        conn.setConnectTimeout(5000);
                        //開啟連線
conn.connect();
                        //連線成功
if (conn.getResponseCode() == 200) {
                            //獲取輸入流物件,此時請求的為一個圖片物件
InputStream is = conn.getInputStream();
                            //儲存檔案到快取
//建立檔案
FileOutputStream fos = new FileOutputStream(file);
                            int lens = 0;
                            byte[] bytes = new byte[1024];
                            while ((lens = is.read(bytes)) != -1) {
                                fos.write(bytes, 0, lens);
                            }
                            fos.close();

                            Bitmap bm= BitmapFactory.decodeFile(file.getAbsolutePath());
                            //利用訊息處理機制傳送給主執行緒，請求更新UI
Message ms = handler.obtainMessage();
                             ms.obj=bm;
                            ms.what = 0;
                            handler.sendMessage(ms);
                        }
                        else {
                            Message ms = handler.obtainMessage();
                            ms.what = 1;
                            handler.sendMessage(ms);
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }


                }
            }.start();
        }
    }
    public String getFileName(String path){
        int index=path.lastIndexOf("/");
        return path.substring(index+1);
    }
}

三.佈局檔案

<?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:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="study.com.cacheinternet.MainActivity">
    <Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="New Button"
android:id="@+id/button"
android:onClick="click"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"/>
    <ImageView
android:layout_width="200dp"
android:layout_height="200dp"
android:id="@+id/imageView"
android:layout_centerVertical="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"/>
</RelativeLayout>

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