按一次可在webView中截取返回按钮，按两次则可退出

import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private WebView webView;
    private long lastBackPressTime = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        webView = findViewById(R.id.webView);
        webView.setWebViewClient(new WebViewClient());

        // 加载网页
        webView.loadUrl("https://www.example.com");
    }

    @Override
    public void onBackPressed() {
        if (webView.canGoBack()) {
            // 如果当前处于webView中，则截取返回按钮事件
            webView.goBack();
        } else {
            // 如果不在webView中，则执行默认的返回操作
            long currentTime = System.currentTimeMillis();
            if (currentTime - lastBackPressTime > 2000) {
                Toast.makeText(this, "再按一次退出", Toast.LENGTH_SHORT).show();
                lastBackPressTime = currentTime;
            } else {
                super.onBackPressed();
            }
        }
    }
}