demo代码如下

package wang.qiaoce.webtest;

import android.content.Context;
import android.os.Build;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.webkit.JavascriptInterface;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.TextView;

public class WebTest extends AppCompatActivity {
    private WebView webview;
    private TextView testTxt;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_web_test);
        testTxt = (TextView)findViewById(R.id.testTxt);
        webview = (WebView)findViewById(R.id.webView);
        WebSettings webSettings = webview.getSettings();
        webSettings.setJavaScriptEnabled(true);
        webview.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);
        webview.setWebViewClient(new WebViewClient(){
            @Override
            public boolean shouldOverrideUrlLoading(WebView view, String url) {
                view.loadUrl(url);
                return true;
            }
        });
        if (Build.VERSION.SDK_INT >= 19) {
            webview.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);
        }
        webview.addJavascriptInterface(new jsApi(),"test");
        webview.loadUrl("file:///android_asset/index.html");
    }
    class jsApi {
        @JavascriptInterface
        public void hello(String htmlContent) {
            testTxt.setText(htmlContent);
        }
    }
}

权限添加

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>