Android Studio - 如何检索网页的内容？

Question

所以我的任务是创建一个经常使用网络服务的安卓应用。

我是 android 和 java 的新手，但我不明白为什么这不起作用。有人可以帮忙吗？在这一点上，我要做的就是记录网站的 html 代码，在这种情况下是谷歌。

MainActivity.java

    package com.dummies.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import android.util.Log;
import com.dummies.myapplication.WebService;
public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        String contents = WebService.getContents("http://www.google.com", "utf-8");
        Log.d("Jon", contents);


        setContentView(R.layout.activity_main);
    }

    public void invokeWS(){

    }
}

WebService.java

    package com.dummies.myapplication;



import android.util.Log;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import android.util.Log;

class WebService {
    public static String getContents(String url, String encodeType) {
        URL u;
        StringBuilder builder = new StringBuilder();
        try {
            u = new URL(url);
            try {
                BufferedReader theHTML = new BufferedReader(new InputStreamReader(u.openStream(), encodeType));
                String thisLine;
                while ((thisLine = theHTML.readLine()) != null) {
                    builder.append(thisLine).append("\n");
                }
            } catch (Exception e) {
                Log.d("Jon", "Error 2");

            }
        } catch (MalformedURLException e) {
            Log.d("Jon", "Error");
            System.err.println(url + " is not a parseable URL");
            System.err.println(e);
        }
        return builder.toString();
    }
}

我在日志中不断出现错误 2，这是为什么呢？有人可以帮助使此代码正常工作并记录输出。 谢谢！

堆栈：

02-03 23:41:56.261 2297-2297/com.dummies.myapplication D/Jon: Stack Trace:
02-03 23:41:56.262 2297-2297/com.dummies.myapplication W/System.err: android.os.NetworkOnMainThreadException
02-03 23:41:56.262 2297-2297/com.dummies.myapplication W/System.err:     at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1303)
02-03 23:41:56.262 2297-2297/com.dummies.myapplication W/System.err:     at java.net.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:86)
02-03 23:41:56.262 2297-2297/com.dummies.myapplication W/System.err:     at java.net.Inet6AddressImpl.lookupAllHostAddr(Inet6AddressImpl.java:74)
02-03 23:41:56.262 2297-2297/com.dummies.myapplication W/System.err:     at java.net.InetAddress.getAllByName(InetAddress.java:752)
02-03 23:41:56.262 2297-2297/com.dummies.myapplication W/System.err:     at com.android.okhttp.internal.Network$1.resolveInetAddresses(Network.java:29)
02-03 23:41:56.262 2297-2297/com.dummies.myapplication W/System.err:     at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:187)
02-03 23:41:56.262 2297-2297/com.dummies.myapplication W/System.err:     at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:156)
02-03 23:41:56.262 2297-2297/com.dummies.myapplication W/System.err:     at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:98)
02-03 23:41:56.262 2297-2297/com.dummies.myapplication W/System.err:     at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:345)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:328)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:246)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:457)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at com.android.okhttp.internal.huc.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:405)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at com.android.okhttp.internal.huc.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:243)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at java.net.URL.openStream(URL.java:1057)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at com.dummies.myapplication.WebService.getContents(WebService.java:22)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at com.dummies.myapplication.MainActivity.onCreate(MainActivity.java:23)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at android.app.Activity.performCreate(Activity.java:6662)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at android.app.ActivityThread.-wrap12(ActivityThread.java)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:102)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at android.os.Looper.loop(Looper.java:154)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:6077)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
02-03 23:41:56.263 2297-2297/com.dummies.myapplication W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
02-03 23:41:56.527 1278-1484/? E/SurfaceFlinger: ro.sf.lcd_density must be defined as a build property

                                                 [ 02-03 23:41:56.529  2297: 2297 D/         ]
                                                 HostConnection::get() New Host Connection established 0xa4a93200, tid 2297


                                                 [ 02-03 23:41:56.530  2297: 2297 W/         ]
                                                 Process pipe failed
02-03 23:41:56.556 1278-1318/? D/gralloc_ranchu: gralloc_alloc: format 1 and usage 0x900 imply creation of host color buffer

                                                 [ 02-03 23:41:56.557  2297: 2413 D/         ]
                                                 HostConnection::get() New Host Connection established 0xa4a93600, tid 2413
02-03 23:41:56.563 2297-2413/com.dummies.myapplication I/OpenGLRenderer: Initialized EGL, version 1.4
02-03 23:41:56.563 2297-2413/com.dummies.myapplication D/OpenGLRenderer: Swap behavior 1
02-03 23:41:56.564 1278-1318/? D/gralloc_ranchu: gralloc_alloc: format 1 and usage 0x900 imply creation of host color buffer
02-03 23:41:56.572 1278-1318/? D/gralloc_ranchu: gralloc_alloc: format 1 and usage 0x900 imply creation of host color buffer
02-03 23:41:56.594 2297-2413/com.dummies.myapplication E/EGL_emulation: tid 2413: eglSurfaceAttrib(1146): error 0x3009 (EGL_BAD_MATCH)
02-03 23:41:56.594 2297-2413/com.dummies.myapplication W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0x98224160, error=EGL_BAD_MATCH
02-03 23:41:56.603 2271-2271/com.google.android.googlequicksearchbox:search W/art: Long monitor contention with owner Binder:2271_1 (2283) at void java.lang.Object.wait!()(Object.java:-2) waiters=0 in java.lang.Object a.a.c.get() for 470ms
02-03 23:41:56.641 1569-1592/system_process I/ActivityManager: Displayed com.dummies.myapplication/.MainActivity: +6s119ms
02-03 23:41:56.655 1569-1693/system_process I/WindowManager: Destroying surface Surface(name=com.android.launcher3/com.android.launcher3.Launcher) called by com.android.server.wm.WindowStateAnimator.destroySurface:2014 com.android.server.wm.WindowStateAnimator.destroySurfaceLocked:881 com.android.server.wm.WindowState.destroyOrSaveSurface:2073 com.android.server.wm.AppWindowToken.destroySurfaces:363 com.android.server.wm.AppWindowToken.notifyAppStopped:389 com.android.server.wm.WindowManagerService.notifyAppStopped:4456 com.android.server.am.ActivityStack.activityStoppedLocked:1252 com.android.server.am.ActivityManagerService.activityStopped:6895 
02-03 23:41:56.669 2271-2414/com.google.android.googlequicksearchbox:search W/ModelDownloadController: Cannot find any speech config location.

Answer 1

问题在于 Android 不允许您在发生 UIOperations 的同一线程上执行网络操作。

为了连接到网络，您必须使用 AsyncTasks 或服务创建不同的线程。

这里有一个关于 Android 网络的更详细的答案：How to fix android.os.NetworkOnMainThreadException?

Answer 2

也许你应该使用 Jsoup 库。太酷了。您可以在此处找到更多信息。

https://jsoup.org/