无需手动撰写，HarmonyOS工具自动生成代码，真香！

// 定义JS模板生成路径
def jsOutputDir = project.file("src/main/js/default/generated").toString()
ohos {
    defaultConfig {
        javaCompileOptions {
            annotationProcessorOptions {
                // JS模板代码生成路径赋值
                arguments = ['jsOutputDir': jsOutputDir] 
            }
        }
    }
}
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ohos {
    compileOptions {
        // 此处为启用js2java-codegen工具的开关。值为true则启用工具，false则不启用工具。
        f2pautogenEnabled true
    }
}
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package com.example.simplecalculatorfapa;
import com.example.simplecalculatorfapa.utils.Util;
import ohos.annotation.f2pautogen.InternalAbility;
import java.util.EmptyStackException;
import java.util.regex.Pattern;
// 注册到同一个包下的MainAbility类中
@InternalAbility(registerTo = "com.example.simplecalculatorfapa.MainAbility")
public class CalculateService {
    public String calculate(String exp) {
        // 排除不需计算就可发现的非法情况，此处列出一种为例
        if (exp.isEmpty()) {
            return "NoResult";
        }
        // ...
        // 使用工具类进行计算，捕获可能出现的异常
        String result;
        try {
            result = Util.getResult(exp);
        } catch (NumberFormatException | ArithmeticException | EmptyStackException e) {
            return "Wrong";
        }
        // 返回合法结果
        return result;
    }
}
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public boolean onRemoteRequest(int code,MessageParcel data, MessageParcel reply,
    MessageOption option) {
  Map<String, Object> result = new HashMap<String,Object>();
  switch(code) {
    case OPCODE_calculate:{
    java.lang.String zsonStr =data.readString();
    ZSONObject zsonObject =ZSONObject.stringToZSON(zsonStr);
    java.lang.String exp =zsonObject.getObject("exp",java.lang.String.class);
    result.put("code", SUCCESS);
    result.put("abilityResult",service.calculate(exp));
    break;}
    default:reply.writeString("Opcode is not defined!");
    return false;
  }
  return sendResult(reply,result, option.getFlags() == MessageOption.TF_SYNC);
}
rivate boolean sendResult(MessageParcel reply,Map<String, Object> result, boolean isSync) {
  if (isSync) {
   reply.writeString(ZSONObject.toZSONString(result));
  } else {
    MessageParcel response =MessageParcel.obtain();
   response.writeString(ZSONObject.toZSONString(result));
    IRemoteObject remoteReply =reply.readRemoteObject();
    try {
      remoteReply.sendRequest(0, response,MessageParcel.obtain(), new MessageOption());
      response.reclaim();
    } catch (RemoteExceptionexception) {
      return false;
    }
  }
  return true;
}
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// This file is automatically generated. Do not modify it!
const ABILITY_TYPE_EXTERNAL = 0;
const ABILITY_TYPE_INTERNAL = 1;
const ACTION_SYNC = 0;
const ACTION_ASYNC = 1;
const BUNDLE_NAME = 'com.example.simplecalculatorfapa';
const ABILITY_NAME = 'com.example.simplecalculatorfapa.CalculateServiceStub';
const OPCODE_calculate = 0;
const sendRequest = async (opcode, data) => {
    var action = {};
    action.bundleName = BUNDLE_NAME;
    action.abilityName = ABILITY_NAME;
    action.messageCode = opcode;
    action.data = data;
    action.abilityType = ABILITY_TYPE_INTERNAL;
    action.syncOption = ACTION_SYNC;
    return FeatureAbility.callAbility(action);
}
class CalculateService {
   async calculate(exp) {
      if (arguments.length != 1) {
         throw new Error("Method expected 1 arguments, got " + arguments.length);
      }
      let data = {};
      data.exp = exp;
      const result = await sendRequest(OPCODE_calculate, data);
      return JSON.parse(result);
   }
}
export default CalculateService;
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// 引入calculateService类
import CalculateService from '../../generated/CalculateService.js';  
export default {
    // 用于实现输入框和结果框的动态变化
    data: {
        input: "",  // 输入框内容
        result: ""  // 结果框内容
    },
    // 不需要调用PA的按钮功能实现，此处列出退格键为例
    deleteOne() {
        this.result = "";
        this.input = this.input.substr(0, this.input.length-1);
    },
    // ...
    // 由等号触发的方法，调用PA
    calculate() {
        // 新建CalculateService示例
        var service = new CalculateService();  
        // 调用calculate方法，传入输入框内容并将返回结果赋值给结果框
        service.calculate(this.input)  
        .then((data) => {
            this.result = data["abilityResult"];
        });
    }
}
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