【Android网络编程】获取网络图片，具有缓存功能

<?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=".MainActivity">    <TextView android:text="查看网络图片" android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:id="@+id/textView" />    <ImageView        android:layout_width="match_parent"        android:layout_height="300dp"        android:id="@+id/imageView"        android:layout_below="@+id/textView"        android:layout_alignParentLeft="true"        android:layout_alignParentStart="true" />    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="下载图片"        android:id="@+id/button"        android:layout_below="@+id/imageView"        android:layout_alignParentLeft="true"        android:layout_alignParentStart="true" /></RelativeLayout>

package qindachang.internetdemo;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.Handler;import android.os.Message;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.ImageView;import android.widget.Toast;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;public class MainActivity extends AppCompatActivity {    private ImageView imageView;    private Button button;    private MyThread myThread;    private Bitmap bitmap;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        imageView = (ImageView) findViewById(R.id.imageView);        button = (Button) findViewById(R.id.button);        button.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                myThread = new MyThread();                myThread.start();            }        });    }    private void GetInternetImg() {        //下载图片        //1.确定网址        String path = "http://img2.imgtn.bdimg.com/it/u=1031079800,2914158222&fm=21&gp=0.jpg";        //②带缓存功能的读取        File file = new File(getCacheDir(), getFileName(path));        //如果缓存存在        if (file.exists()) {            //从缓存中读取图片            bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());            mHandler.sendEmptyMessage(0);        } else {            //2.把网址封装成url对象            try {                URL url = new URL(path);                //3.获取客户端和服务器的连接对象，此时还没有建立连接，这时候还没有任何的网络交互                HttpURLConnection connection= (HttpURLConnection) url.openConnection();                //4.对连接对象进行初始化                //设置请求方法                connection.setRequestMethod("GET");                //设置连接超时时间                connection.setConnectTimeout(5000);                //设置读取超时                connection.setReadTimeout(3000);                //5.发送请求，与服务器建立连接，这段代码一旦执行，就会有网络交互了                connection.connect();                //如果响应码为200，说明请求成功                if (connection.getResponseCode() == 200) {                    //获取服务器响应头中的流，流里的数据就是客户端请求的数据                    InputStream is = connection.getInputStream();                    //从流里读数据,安卓有一个API可以从流里直接读取图片                    FileOutputStream fos = new FileOutputStream(file);                    byte[] bytes = new byte[1024];                    int len = 0;                    while ((len = is.read(bytes)) != -1) {                        fos.write(bytes, 0, len);                    }                    fos.close();                    bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());                    //①从里读取数据，并构造成位图对象//                bitmap = BitmapFactory.decodeStream(is);                    mHandler.sendEmptyMessage(0);                } else {                    Toast.makeText(MainActivity.this,"请求失败",Toast.LENGTH_SHORT).show();                }            } catch (MalformedURLException e) {                e.printStackTrace();            } catch (IOException e) {                e.printStackTrace();            }        }    }    private Handler mHandler = new Handler(new Handler.Callback() {        @Override        public boolean handleMessage(Message msg) {            imageView.setImageBitmap(bitmap);            return false;        }    });    private class MyThread extends Thread {        @Override        public void run() {            super.run();            GetInternetImg();        }    }    private String getFileName(String path) {        String[] name = path.split(",");        return name[1];    }}
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