Android使用OkHttp框架下載網絡圖片

一、OkHttp簡介

OkHttp是一款優秀的HTTP框架，它支持get請求和post請求，支持基於Http的文件上傳和下載，支持加載圖片，支持下載文件透明的GZIP壓縮，支持響應緩存避免重複的網絡請求，支持使用連接池來降低響應延遲問題。

OkHttp官網地址：http://square.github.io/okhttp/
OkHttp GitHub地址：https://github.com/square/okhttp

Android Studio中OkHttp的配置方法：
在GRADLE中添加

    compile 'com.squareup.okhttp3:okhttp:3.4.1'
    compile 'com.squareup.okio:okio:1.11.0'

注意：okhttp內部依賴okio，所以同時還需要導入okio：

二、OkHttp的基本使用

1、Requests
每一個HTTP請求中都應該包含一個URL，一個GET或POST方法以及Header或其他參數，當然還可以含特定內容類型的數據流。

public final class Request {
  private final HttpUrl url;
  private final String method;
  private final Headers headers;
  private final RequestBody body;
  private final Object tag;
  ... ...
  }

2、Responses

響應則包含一個回覆代碼（200代表成功，404代表未找到），Header和定製可選的body。

public final class Response implements Closeable {
  private final Request request;
  private final Protocol protocol;
  private final int code;
  private final String message;
  private final Handshake handshake;
  private final Headers headers;
  private final ResponseBody body;
  private final Response networkResponse;
  private final Response cacheResponse;
  private final Response priorResponse;
  private final long sentRequestAtMillis;
  private final long receivedResponseAtMillis;
  ... ...
  }

在日常開發中最常用到的網絡請求就是GET和POST兩種請求方式。

三、OkHttp的GET網絡請求方法

1、異步get

    /**
     * 異步get,直接調用
     */
    private final String IMAGE_URL = "...";
    private OkHttpClient client;

    private void asyncGet() {
        client = new OkHttpClient();
        final Request request = new Request.Builder().get()
                .url(IMAGE_URL)
                .build();

        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                e.printStackTrace();

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {

                //......
            }
        });
    }

2、同步get

    /**
     * 同步寫法，需要放在子線程中使用
     */
    private final String IMAGE_URL = "...";
    private OkHttpClient client;

    private void synchronizedGet() {
        client = new OkHttpClient();
        final Request request = new Request.Builder().get()
                .url(IMAGE_URL)
                .build();

        try {
            Response response = client.newCall(request).execute();
            Message message = handler.obtainMessage();
            if (response.isSuccessful()) {
               //......
            } else {
               //......
            }

        } catch (IOException e) {
            e.printStackTrace();
        }

    }

由於Android本身是不允許在UI線程做網絡請求操作的，所以我們自己寫個線程完成網絡操作:

 new Thread(new Runnable() {
            @Override
            public void run() {
                   synchronizedGet();
            }
 }).start();

四、案例：使用OkHttp的get方式下載網絡圖片

Demo源碼下載地址：
http://download.csdn.net/detail/wei_zhi/9672863

首先是一個佈局文件，一個Button和一個ImageView：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp"
    tools:context="com.wz.okhttpdemo.MainActivity">

    <Button
        android:text="下載圖片"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true"
        android:id="@+id/button"
        android:layout_alignParentEnd="true" />

    <ImageView
        android:id="@+id/imageview"
        android:paddingTop="40dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/button"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
 />
</RelativeLayout>

然後是主方法：

package com.wz.okhttpdemo;

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 java.io.IOException;

import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public class MainActivity extends AppCompatActivity {
    private final String IMAGE_URL = "http://cdnq.duitang.com/uploads/item/201505/20/20150520102944_CiL3M.jpeg";

    private static final int IS_SUCCESS = 1;
    private static final int IS_FAIL = 0;

    private Button button;
    private ImageView imageView;

    private OkHttpClient client;

    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case IS_SUCCESS:
                    byte[] bytes = (byte[]) msg.obj;
                    Bitmap bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
                    imageView.setImageBitmap(bitmap);
                    break;
                case IS_FAIL:
                    break;
                default:
                    break;
            }
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button) this.findViewById(R.id.button);
        imageView = (ImageView) this.findViewById(R.id.imageview);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //使用異步get
                asyncGet();
                //使用同步get
  /*              new Thread(new Runnable() {
                    @Override
                    public void run() {
                        synchronizedGet();
                    }
                }).start();*/
            }
        });

    }


    /**
     * 異步get,直接調用
     */
    private void asyncGet() {
        client = new OkHttpClient();
        final Request request = new Request.Builder().get()
                .url(IMAGE_URL)
                .build();

        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                e.printStackTrace();

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {

                Message message = handler.obtainMessage();
                if (response.isSuccessful()) {
                    message.what = IS_SUCCESS;
                    message.obj = response.body().bytes();
                    handler.sendMessage(message);
                } else {
                    handler.sendEmptyMessage(IS_FAIL);
                }
            }
        });
    }

    /**
     * 同步寫法，需要放在子線程中使用
     */
    private void synchronizedGet() {
        client = new OkHttpClient();
        final Request request = new Request.Builder().get()
                .url(IMAGE_URL)
                .build();

        try {
            Response response = client.newCall(request).execute();
            Message message = handler.obtainMessage();
            if (response.isSuccessful()) {
                message.what = IS_SUCCESS;
                message.obj = response.body().bytes();
                handler.sendMessage(message);
            } else {
                handler.sendEmptyMessage(IS_FAIL);
            }

        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}

運行結果：

點擊下載圖片：

OK，這就簡單的實現了使用OkHttp來下載圖片。

Demo源碼下載地址：
http://download.csdn.net/detail/wei_zhi/9672863

參考：
http://m.2cto.com/net/201605/505364.html

http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2015/0824/3355.html