Android 网络图片获取原理

现在的手机以离不开网络了，而且网络速度也越来越快，所以网络HTTP协议请求是必不可少的，现在我们 简单讲解一下网路图片的获取，这里只是讲解一下获取原理，并不是造轮子给大家用，最后会推荐几个轮子给大家用。

逻辑：

1. 首先需要一个图片地址的URL
2. 然后需要通过HTTP网络请求协议在线获取图片
3. 再将图片转换成一个 Bitmap（这里用Bitmap）
4. 在将图片展示到控件上

Activity代码：

package com.example.administrator.foundationdemo.http;

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.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;

import com.example.administrator.foundationdemo.R;
import com.example.administrator.foundationdemo.http.service.ImageService;

import java.io.IOException;

public class HttpImageActivity extends AppCompatActivity {

    private EditText http_image_edittext;
    private Button http_image_button;
    private ImageView http_image_imageview;

    private String urlString = "http://upload-images.jianshu.io/upload_images/4047773-f6c7549ab7c95bd2?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_http_image);
        init();
    }

    private void init(){

        http_image_edittext = (EditText) findViewById(R.id.http_image_edittext);
        http_image_imageview = (ImageView) findViewById(R.id.http_image_imageview);
        http_image_button = (Button) findViewById(R.id.http_image_button);
        http_image_edittext.setText(urlString);

        http_image_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                setImage();
            }
        });
    }
    //开启子线程，进行耗时操作
    private void setImage(){
        Log.d("FLY","请求失败1");
        new Thread(new Runnable() {
            @Override
            public void run() {
                String path = http_image_edittext.getText().toString();
                byte[] date = new byte[0];
                try {
                    date = ImageService.getImage(urlString);
                } catch (IOException e) {
                    e.printStackTrace();
                    Log.d("FLY", "获取图片异常\n" + e.toString());
                    Toast.makeText(HttpImageActivity.this,"获取图片失败",Toast.LENGTH_SHORT).show();
                }
                Log.d("FLY","请求失败1");
                Bitmap bitmap = BitmapFactory.decodeByteArray(date,0,date.length);
                Message msg = new Message();
                msg.obj = bitmap;
                hadler.sendMessage(msg);
            }
        }).start();


    }

    Handler hadler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            Log.d("FLY", "请求失败2");
            Bitmap bitmap = (Bitmap) msg.obj;
            http_image_imageview.setImageBitmap(bitmap);
        }
    };

}

ImageService代码：

package com.example.administrator.foundationdemo.http.service;

import android.util.Log;
import android.widget.Toast;

import com.example.administrator.foundationdemo.http.tool.StreamTool;

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

/**
 * Created by Administrator on 2016/12/29.
 */
public class ImageService {

    public static byte[] getImage(String path) throws IOException {
        URL url = new URL(path);
        HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();//得到基于HTTP协议的链接对象
        httpURLConnection.setConnectTimeout(5000);//请求超时时间
        httpURLConnection.setRequestMethod("GET");//请求方式

        if (httpURLConnection.getResponseCode() == 200){
            InputStream inputStream = httpURLConnection.getInputStream();
            return StreamTool.readInputStream(inputStream);
        }else {
            Log.d("FLY","请求失败"+httpURLConnection.getResponseCode());
        }
        return null;
    }
}

StreamTool 代码：

package com.example.administrator.foundationdemo.http.tool;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * Created by Administrator on 2017/1/3.
 */
public class StreamTool {
    public static byte[] readInputStream(InputStream inputStream) throws IOException {
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        byte[] bytes = new byte[1024];
        int bytrsLen = 0;
        while((bytrsLen =inputStream.read(bytes)) != -1){
            outputStream.write(bytes,0,bytrsLen);
        }
        inputStream.close();
        return outputStream.toByteArray();
    }
}

XML代码：

说好的向大家推荐几个很好用的轮子：

1. Picasso

2. Fresco