关于WebView加载网页的注意：
1、覆盖webView使用本地系统浏览器或者第三方
2、物理返回键返回网页
3、加载网页进度条
4、网页加载优化，优先使用缓存
5、请事先注册用户Internet权限
下面给出代码（注释详情）：
main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >   
<WebView 
    android:id="@+id/webView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    />
</LinearLayout>

MainActivity.java

package com.example.day101903;

import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.view.KeyEvent;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class MainActivity extends Activity {

    private ProgressDialog progressDialog;
    private WebView webView;
    private String url = "http://www.baidu.com";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
          //跳转网页
//        Uri uri = Uri.parse(url);
//        Intent intent = new Intent(Intent.ACTION_VIEW,uri);
//        startActivity(intent);
        
        webView = (WebView) findViewById(R.id.webView);
        webView.loadUrl("http://www.baidu.com");
        //覆盖webView使用浏览器打开网页
        webView.setWebViewClient(new WebViewClient(){
            @Override
            public boolean shouldOverrideUrlLoading(WebView view, String url) {
                //返回值true为webview打开，false为第三方打开
                view.loadUrl(url);
                return true;
            }
        });
        //启用JavaScript
        WebSettings webSettings = webView.getSettings();
        webSettings.setJavaScriptEnabled(true);
       //webView优先使用缓存
        webSettings.setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);
        
        //监听网页加载进度
        webView.setWebChromeClient(new WebChromeClient(){
            @Override
            public void onProgressChanged(WebView view, int newProgress) {
                
            //newProgress为0-100的整数
            if(newProgress==100){
                //网页加载完毕
                closeDialog();
            }else{
                //网页正在加载
                openDialog(newProgress);
            }
            }

            private void openDialog(int newProgress) {
                if(progressDialog==null){
                    progressDialog = new ProgressDialog(MainActivity.this);
                    progressDialog.setTitle("正在加载");
                    progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
                    progressDialog.setProgress(newProgress);
                    progressDialog.show();
                }else{
                    progressDialog.setProgress(newProgress);
                }
                
            }

            private void closeDialog() {
                if(progressDialog!=null&&progressDialog.isShowing()){
                    progressDialog.dismiss();
                    progressDialog=null;
                }
                
            }
        });
        
        
    }
    
    //改写物理键返回的逻辑
    
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if(keyCode==KeyEvent.KEYCODE_BACK){
            if(webView.canGoBack()){
                webView.goBack();
                return true;
            }
            else{
                System.exit(0);
            }
        }
            
        
        return super.onKeyDown(keyCode, event);
    }
   
}

演示效果（截图时候不知道为什么进不去了，就这样吧~~）：

url.gif