Android调用js代码:

webview.loadUrl("javascript:fun()")

js调用java代码：

getSettings().setJavaScriptEnabled(true);
addJavascriptInterface(new JsHandel(), "jsApi");

public class JsHandel {
    @JavascriptInterface
    public void call(String dataObj) {
    }
}

     不过这种只能简单的相互调用而已，如果需要回调（例如：js调用android方法并从android端返回数据）还需要做一定的封装处理才可以，大概实现步骤：
     1. 在android代码中向H5页面注入js对象
     2. js端创建一个存储callback回调函数唯一id、callback回调函数的map键值对对象，当js调用android代码时，生成一个callback回调函数唯一id，把该callback回调函数的唯一id和callback回调函数存放到map对象中，并把callback回调函数唯一id传递给android端
      3. android端执行js调用并获取到callback回调函数唯一id，调用js代码将执行结果数据和callback回调函数唯一id传递给js端
     4. js端遍历map对象并根据回调函数唯一id找到对应的callback回调函数，通过callback.call(null, data)执行该js回到函数

     至此js调用android代码并完成回调，具体代码如下：

1. 在android代码中向H5页面注入js对象

	//MainActivity.java
	@Override
    public void initView() {
        binding.webview.registHandel("gjsbridgeApi", new JsHandel() {
            @Override
            public void jscall(String funName, String funData, JsFunctionCallBack jsFunction) {
                if("getVolumn".equals(funName)){
                    VolumnApi volumnApi = new VolumnApi();
                    jsFunction.callback(volumnApi.getVolumn(MainActivity.this));
                    return;
                }else if("showToast".equals(funName) && funData!=null && !funData.isEmpty()){
                    Toast.makeText(MainActivity.this, funData, Toast.LENGTH_LONG).show();
                    return;
                }
                jsFunction.callback("from native");
            }
        });
        binding.webview.loadUrl("http://pojul.gitee.io/web/testjsbridge/");
    }

	//GjsbridgeWebview.java
	public void registHandel(String handelName, JsHandel jsHandel){
        if(jsHandel==null){
            return;
        }
        jsHandel.init(this);
        getSettings().setJavaScriptEnabled(true);
        addJavascriptInterface(jsHandel, handelName);
 	}

//JsHandel.java
public abstract class JsHandel {
    private static final String TAG = "JsHandel";
    private GjsbridgeWebview gjsbridgeWebview;

    public void init(GjsbridgeWebview gjsbridgeWebview){
        this.gjsbridgeWebview = gjsbridgeWebview;
    }

    @JavascriptInterface
    public void call(String dataObj) {
        JsFun jsFun = new Gson().fromJson(dataObj, JsFun.class);
        if(jsFun.funName==null||jsFun.funName.isEmpty()){
            return;
        }
        JsFunctionCallBack jsFunction = new JsFunctionCallBack(jsFun.funId) {
            @Override
            public void callback(String respData) {
                if(gjsbridgeWebview==null){
                    Log.e(TAG, "gjsbridgeWebview has not init");
                    return;
                }
                if(funId==null||funId.isEmpty()){
                    return;
                }
                gjsbridgeWebview.post(() -> {
                    gjsbridgeWebview.loadUrl("javascript:gjsbridgeApiCallBack('"+funId+"', '"+respData+"')");
                });
            }
        };
        jscall(jsFun.funName, jsFun.funData, jsFunction);
    }

    public abstract void jscall(String funName, String funData, JsFunctionCallBack jsFunction);
}

//JsFun.java
public class JsFun {
    public String funId;
    public String funName;
    public String funData;
}

2. js端创建map并执行callback.call(null, data)代码

//api.js
class Api{
    constructor(){
    }
    showToast(msg){
    	call("showToast", msg, null);
    }
    getVolumn(fun){
    	call("getVolumn", null, fun);
    }
}

var api = new Api();
var funMap = new Map();
function gjsbridgeApiCallBack(funId, data){
    console.log("H5 gjsbridgeApiCallBack funId: " + funId + "; data: " + data);
    let fun = funMap.get(funId);
    if(fun!=null){
    	fun.call(null, data);
    }
    funMap.delete(funId);
    console.log("funMap size: " + funMap.size)
}

function call(name, data, fun){
	if(window.gjsbridgeApi==null){
    	console.log(name + "; H5 window.gjsbridgeApi: null");
    }else{
    	console.log(name + "; H5 window.gjsbridgeApi: " + window.gjsbridgeApi);
    	let dataObj = {
			funName: name,
			funData: data
		}
		if(fun!=null && typeof fun === "function"){
		    let funId = Date.now()+"";
		    funMap.set(funId, fun);
		    dataObj.funId = funId;
	    }
    	window.gjsbridgeApi.call(JSON.stringify(dataObj));
    }
}

3. H5直接调用

	//test.html
	<body>
		<div class="toast-div" id="show" onclick="showToast()">toast</div>
		<div class="toast-div" id="volumn" onclick="getVolumn()">volumn: unknow</div>
	</body>

	<script type="text/javascript">
		function showToast(){
			api.showToast("toast-div click");
		}
		function getVolumn(){
			api.getVolumn(function(data){
				console.log("getVolumn: " + data);
				document.getElementById("volumn").innerHTML = data;
			});
		}
	</script>

demo地址: https://github.com/pojul/gjsbridge：
gjsbridge集成：implementation ‘io.github.pojul:gjsbridge:1.0.1’