【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];
    }
}