How to use opcua protocol on appinventor?

Here is an inexplicable need , So it's not easy to find tutorials online , So I stepped on some pits .

Because I'm not familiar with java, It's also stumbling .

opcua Library selection

First opcua I found two ：

1.https://github.com/eclipse/milohttps://github.com/eclipse/milo

2.GitHub - OPCFoundation/UA-Java-Legacy: This repository is provided by OPC Foundation as legacy support for an Java version for OPC UA.https://github.com/OPCFoundation/UA-Java-Legacy

The new is the good principle , Used milo, There are many online tutorials , But there was a pit .

because milo It's a newer version of java Development , The features of the new version are not applicable to the old version ！

and appinventor It is a project with a very early development time , Supported by java The version is 7/8.

In the step of importing and compiling appinventor Development _ Taoist incense's blog -CSDN Blog Reference documents ：https://saitwalshreyash19.medium.com/writing-extensions-for-app-inventor-2-and-kodular-7d20092bff16https://saitwalshreyash19.medium.com/writing-extensions-for-app-inventor-2-and-kodular-7d20092bff16https://islet.blog.csdn.net/article/details/124301948?spm=1001.2014.3001.5502 But it keeps reporting mistakes ！

I found out later because milo Used lambda characteristic , As a result, the library is not supported .

So in the end I chose OPCFoundation This , Can be published in tag Download directly from .jar file , It's relatively simple .

Library import problem

But even so , There will still be problems , Because the library also relies on sl4j This .

Due to initial contact java, I don't know why this library is used , But you can find some solutions on the Internet , Go directly to download ：

Pay attention to the version I use , Even if it is opcua You can't use too new versions , If you choose wrong, there will be compilation errors .

Then pay attention to java Both libraries are required when importing from a file ：

@SimpleObject(external = true) // External plug-ins 
// You can't put it in this position ！ Must be in SimpleObject below 
@UsesLibraries(libraries = "opc-ua-stack-1.4.1-224.jar,slf4j-api-1.7.0.jar")

Development process

there import Not very professional , Add everything you may need ：

// opcua
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.InetAddress;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.UnrecoverableKeyException;
import java.security.cert.Certificate;
import java.security.cert.CertificateEncodingException;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.security.interfaces.RSAPrivateKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.InvalidParameterSpecException;

import javax.crypto.BadPaddingException;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;


import java.util.Locale;
import com.google.appinventor.components.annotations.UsesLibraries;
import org.opcfoundation.ua.application.Client;
import org.opcfoundation.ua.application.SessionChannel;
import org.opcfoundation.ua.builtintypes.LocalizedText;
import org.opcfoundation.ua.builtintypes.NodeId;
import org.opcfoundation.ua.cert.CertificateCheck;
import org.opcfoundation.ua.cert.DefaultCertificateValidator;
import org.opcfoundation.ua.cert.DefaultCertificateValidatorListener;
import org.opcfoundation.ua.cert.PkiDirectoryCertificateStore;
import org.opcfoundation.ua.cert.ValidationResult;
import org.opcfoundation.ua.core.ApplicationDescription;
import org.opcfoundation.ua.core.Attributes;
import org.opcfoundation.ua.core.BrowseDescription;
import org.opcfoundation.ua.core.BrowseDirection;
import org.opcfoundation.ua.core.BrowseResponse;
import org.opcfoundation.ua.core.BrowseResultMask;
import org.opcfoundation.ua.core.Identifiers;
import org.opcfoundation.ua.core.NodeClass;
import org.opcfoundation.ua.core.ReadResponse;
import org.opcfoundation.ua.core.ReadValueId;
import org.opcfoundation.ua.core.TimestampsToReturn;
import org.opcfoundation.ua.common.ServiceResultException;
import org.opcfoundation.ua.transport.security.Cert;
import org.opcfoundation.ua.transport.security.KeyPair;
import org.opcfoundation.ua.transport.security.PrivKey;
import org.opcfoundation.ua.utils.CertificateUtils;


import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


import static org.opcfoundation.ua.utils.EndpointUtil.selectByMessageSecurityMode;
import static org.opcfoundation.ua.utils.EndpointUtil.selectByProtocol;
import static org.opcfoundation.ua.utils.EndpointUtil.sortBySecurityLevel;

import java.net.InetAddress;
import org.opcfoundation.ua.application.Client;
import org.opcfoundation.ua.core.Attributes;
import org.opcfoundation.ua.core.EndpointDescription;
import org.opcfoundation.ua.core.Identifiers;
import org.opcfoundation.ua.core.MessageSecurityMode;
import org.opcfoundation.ua.core.ReadRequest;
import org.opcfoundation.ua.core.ReadResponse;
import org.opcfoundation.ua.core.ReadValueId;
import org.opcfoundation.ua.core.TimestampsToReturn;
import org.opcfoundation.ua.transport.ServiceChannel;
import org.opcfoundation.ua.transport.security.KeyPair;
//write
import org.opcfoundation.ua.builtintypes.DataValue;
import org.opcfoundation.ua.builtintypes.Variant;
import org.opcfoundation.ua.core.WriteResponse;
import org.opcfoundation.ua.core.WriteValue;
import org.opcfoundation.ua.core.WriteRequest;
import org.opcfoundation.ua.core.RequestHeader;

//thread
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

The steps to connect to the server ：

    // Create a task class , similar Runnable  
    public static class CallerTask implements Callable<String>{  
        @Override  
        public String call() throws Exception{
            String retStr = "";  
            Client myClient = Client.createClientApplication(null);
            try {
            String url = "opc.tcp://192.168.1.8:4840";
            SessionChannel mySession = myClient.createSessionChannel(url);
            mySession.activate("username", "passwd.");

            mySession.close();
            mySession.closeAsync();
            
            } catch (Exception e1) {
                retStr = "Error";
            }
            return retStr;
        }  
    }

Threads are used here because the main program cannot use network services .

Read operations ：

ReadResponse res4 = mySession.Read(null, 500.0, TimestampsToReturn.Source,
new ReadValueId(new NodeId(1, "XXXXX"), Attributes.Value, null, null));
            
retStr = String.valueOf(res4.getResults()[0].getValue());//getStatusCode

Write operations ：

NodeId nodeId = new NodeId(1, "XXX");
//Bad_TypeMismatch  double Type must have a decimal point 
DataValue dataValue = new DataValue(new Variant(999.0));
WriteValue writeValue[] = new WriteValue[1];
writeValue[0] = new WriteValue(nodeId, Attributes.Value, null, dataValue); // The third parameter is zero null You can use ordinary writing  
RequestHeader requestHeader = new RequestHeader(nodeId, null, null, null, null, null, null);
WriteRequest writeRequest = new WriteRequest(requestHeader, writeValue);
WriteResponse response = mySession.Write(writeRequest);

retStr = String.valueOf(response.getResults()[0]);//

Finally, add the call of thread return value ：

    public String readNode() throws Exception{
        String retStr = "";
        // Android 4.0  After that... Cannot be requested in the main thread HTTP request 
        // Create asynchronous tasks   
        FutureTask<String> futureTask = new FutureTask<>(new ReadCallerTask());  
        // Start thread   
        new Thread(futureTask).start();  
        try{  
            // Wait for the task to finish , And return the result   
            String result = futureTask.get();  
            return  result;
        } catch (ExecutionException e){  
            e.printStackTrace();  
        } 
        return retStr;
    }