在webview声明后放置zoom方法，请参考以下代码

Put the zoom method after webview declaration,Please refer below code

public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.show_web_view);

        webView = (WebView) findViewById(R.id.webView1);
        WebSettings webSettings = webView.getSettings();
        webSettings.setBuiltInZoomControls(true);
        webSettings.setSupportZoom(true);
}