存放本地html文件：放在app/src/main/assets目录下，一般来说android studio项目下是没有assets文件夹的，所以需要在app/src/main下新建一个文件夹，取名assets；详细步骤请看：[(https://blog.csdn.net/qq_36109644/article/details/82453909)

public class Main4Activity extends AppCompatActivity {
    private WebView webView;
    private ProgressBar progressBar;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main4);
        progressBar= (ProgressBar)findViewById(R.id.progressbar1);//进度条
        webView = (WebView) findViewById(R.id.webview1);

        webView.loadUrl("file:///android_asset/header.html");//加载本地asset文件夹下html

        webView.setWebChromeClient(webChromeClient);
        webView.setWebViewClient(webViewClient);

    }
//WebViewClient主要帮助WebView处理各种通知、请求事件
    private WebViewClient webViewClient=new WebViewClient(){
        @Override
        public void onPageFinished(WebView view, String url) {//页面加载完成
            progressBar.setVisibility(View.GONE);
        }

        @Override
        public void onPageStarted(WebView view, String url, Bitmap favicon) {//页面开始加载
            progressBar.setVisibility(View.VISIBLE);
        }
    };
//WebChromeClient主要辅助WebView处理Javascript的对话框、网站图标、网站title、加载进度等
    private WebChromeClient webChromeClient=new WebChromeClient(){
        @Override
        public void onProgressChanged(WebView view, int newProgress) {
            progressBar.setProgress(newProgress);
        }
    };

    @Override
    protected void onDestroy() {
        super.onDestroy();
//资源释放
        webView.destroy();
        webView=null;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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="match_parent"
        android:layout_height="match_parent"/>

    <ProgressBar
        android:id="@+id/progressbar"
        style="@android:style/Widget.ProgressBar.Horizontal"
        android:layout_width="match_parent"
        android:layout_height="3dip"
        android:max="100"
        android:progress="50"//进度条当前值
        android:visibility="gone"/>
</FrameLayout>