Android入门第55天-在Android里使用OKHttp组件访问网络资源

简介

今天的课程开始进入高级课程类了，我们要开始接触网络协议、设备等领域编程了。在今天的课程里我们会使用OKHttp组件来访问网络资源而不是使用Android自带的URLConnection。一个是OKHttp组件更方便二个是OKHttp组件本身就带有异步回调功能。

下面就进入课程。

课程目标

我们的课程目标有4个点：

1. 使用OKHttp组件；
2. 使用OKHttp组件加载网络图片显示在APP的ImgView里；
3. 使用OKHttp组件加载给定网页代码显示在ScrollView里；
4. 使用OKHttp组件加载给定网页显示在WebView里；

以上过程都为异步加载。

代码前在gradle里要先声明对于OKHttp组件的引用

要使用OKHttp组件，我们必须要在build.gradle中加入以下语句：

implementation 'com.squareup.okhttp3:okhttp:3.10.0'

 以下是加完上述语句后的build.gradle。

 访问网络资源需要给到APP以权限

我们因为要访问网络资源，因此我们需要给到APP以相应的权限。编辑AndroidManifest.xml文件，并加入以下两行声明。

 加完后的AndroidManifest.xml长这样

 代码

菜单res\menu\pop_menu.xml

主UI界面

MainActivity

package org.mk.android.demo.http;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.webkit.WebView;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.PopupMenu;
import android.widget.ScrollView;
import android.widget.TextView;

import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.Charset;
import okhttp3.OkHttpClient;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.ResponseBody;
import okio.Buffer;
import okio.BufferedSource;
public class MainActivity extends AppCompatActivity {

    private String TAG = "DemoOkHttp";
    private Button buttonShowMenu;
    private TextView htmlTxt;
    private ImageView imgPic;
    private WebView webView;
    private ScrollView scroll;
    private Bitmap bitmap;
    private String htmlContents;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        buttonShowMenu = (Button) findViewById(R.id.buttonShowMenu);
        htmlTxt = (TextView) findViewById(R.id.htmlTxt);
        imgPic = (ImageView) findViewById(R.id.imgPic);
        webView = (WebView) findViewById(R.id.webView);
        scroll = (ScrollView) findViewById(R.id.scroll);
        buttonShowMenu.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                PopupMenu popup = new PopupMenu(MainActivity.this, buttonShowMenu);
                popup.getMenuInflater().inflate(R.menu.pop_menu, popup.getMenu());
                popup.setOnMenuItemClickListener(new MenuItemClick());
                popup.show();
            }
        });
    }

    // 定义一个隐藏所有控件的方法:
    private void hideAllWidget() {
        imgPic.setVisibility(View.GONE);
        scroll.setVisibility(View.GONE);
        webView.setVisibility(View.GONE);
    }

    private class MenuItemClick implements PopupMenu.OnMenuItemClickListener {
        @Override
        public boolean onMenuItemClick(MenuItem item) {
            String imgPath = "https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fimg.alicdn.com%2Fi2%2F2542318073%2FO1CN01fJvTi029VTwR16EvP_%21%212542318073.jpg&refer=http%3A%2F%2Fimg.alicdn.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1673938156&t=69e5ee87fbf4b81b5f6eea53ed5b5158";
            String htmlPagePath = "https://www.baidu.com";
            switch (item.getItemId()) {
                case R.id.menuItemDisplayPic:
                    downLoadImgFromPath(imgPath);
                    break;
                case R.id.menuItemDisplayHtmlCode:
                    getHtmlAsync(htmlPagePath, 102);
                    break;
                case R.id.menuItemDisplayHtmlPage:
                    getHtmlAsync(htmlPagePath, 103);

                    break;
            }
            return true;
        }
    }

    private Handler httpHandler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(@NonNull Message msg) {
            Log.i(TAG, ">>>>>>receive handler Message msg.what is: " + msg.what);
            switch (msg.what) {
                case 101:
                    hideAllWidget();
                    imgPic.setVisibility(View.VISIBLE);
                    Log.i(TAG, "begin to show img from bitmap type's data");
                    imgPic.setImageBitmap(bitmap);
                    break;
                case 102:
                    hideAllWidget();
                    Log.i(TAG, "begin to show html contents");
                    scroll.setVisibility(View.VISIBLE);
                    Log.d(TAG, ">>>>>>htmlContents->\n" + htmlContents);
                    htmlTxt.setText(htmlContents);
                    break;
                case 103:
                    hideAllWidget();
                    Log.i(TAG, "begin to show html page in webview");
                    webView.setVisibility(View.VISIBLE);
                    Log.d(TAG, ">>>>>>htmlContents->\n" + htmlContents);
                    webView.loadDataWithBaseURL("", htmlContents, "text/html", "UTF-8", "");
                    break;
            }
            return false;
        }
    });
    /**
     * 使用okhttp 异步下载图片
     */
    private void downLoadImgFromPath(String path) {

        OkHttpClient client = new OkHttpClient();

        Request request = new Request.Builder()
                .url(path)
                .build();
        Log.i(TAG, ">>>>>>into doanloadImgFromPath method");
        try {
            Call call = client.newCall(request); // 使用client去请求

            call.enqueue(new Callback() { // 回调方法，>>> 可以获得请求结果信息
                InputStream inputStream = null;

                @Override
                public void onFailure(Call call, IOException e) {
                    Log.e(TAG, ">>>>>>下载失败", e);
                }

                @Override
                public void onResponse(Call call, Response response) throws IOException {
                    Log.i(TAG, ">>>>>>into onResponse method");
                    try {
                        inputStream = response.body().byteStream();
                        Log.i(TAG, ">>>>>>the response code is: " + response.code());
                        if (200 == response.code()) {
                            bitmap = BitmapFactory.decodeStream(inputStream);
                            Log.i(TAG, ">>>>>>sendEmptyMessage 101 to handler");
                            httpHandler.sendEmptyMessage(101);
                        } else {
                            Log.i(TAG, ">>>>>>下载失败");
                        }
                    } catch (Exception e) {
                        Log.e(TAG, ">>>>>>okHttp onResponse error: " + e.getMessage(), e);
                    } finally {
                        try {
                            inputStream.close();
                        } catch (Exception e) {
                        }
                    }
                }
            });

        } catch (Exception e) {
            Log.e(TAG, ">>>>>>OkHttp调用失败", e);
        }
    }

    //异步不需要创建线程
    private void getHtmlAsync(String path, int handlerCode) {
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder().url(path).build();
        //请求的call对象
        Call call = client.newCall(request);
        //异步请求
        call.enqueue(new Callback() {

            //失败的请求
            @Override
            public void onFailure(@NonNull Call call, @NonNull IOException e) {
                Log.e(TAG, ">>>>>>加载path失败", e);
            }

            //结束的回调
            @Override
            public void onResponse(@NonNull Call call, @NonNull Response response) throws IOException {
                //响应码可能是404也可能是200都会走这个方法
                Log.i(TAG, ">>>>>>the response code is: " + response.code());
                if (200 == response.code()) {
                    try {
                        ResponseBody responseBody = response.body();
                        BufferedSource source = responseBody.source();
                        source.request(Long.MAX_VALUE);
                        Buffer buffer = source.buffer();
                        Charset UTF8 = Charset.forName("UTF-8");
                        htmlContents = buffer.clone().readString(UTF8);
                        Log.i(TAG, ">>>>>>sendEmptyMessage " + handlerCode + " to handler");
                        httpHandler.sendEmptyMessage(handlerCode);
                        Log.i(TAG, "getAsyncHtmlGet成功");
                    } catch (Exception e) {
                        Log.e(TAG, ">>>>>>read htmlPage error: " + e.getMessage(), e);
                    }
                }
            }
        });
    }
}

核心代码导读

我们使用的是

Call call = client.newCall(request);

它本身就是支持异步的一个调用。 然后在得到相应的Http报文后使用一个Handler向APP主界面发起改变界面中内容的调用。

这边有一点需要注意的是OKHttp在返回的response.body()这个API，在一次请求里只能被使用一次。即如果你已经有以下一句类似的调用：

inputStream = response.body().byteStream();

你就不能再在它以下的语句中调用一次response.body()了。

自己动一下手试试看效果吧。