【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];
}
}