Access by variable name

The following program accesses a PLC variable that does not have an address. Access must therefore be made by the variable name.

Unpack the sample program 'Access by Variable Name': sample02.zip.

• To execute the *.jar sample, the command 'java -classpath "Sample02.jar;[path to TcJavaToAds.jar] Main' must be executed in the console in the correct directory (example path: "C:TwinCAT\Ads Api\AdsToJava\*"). For this, java must be entered in the environment variables.

import de.beckhoff.jni.Convert;
import de.beckhoff.jni.JNIByteBuffer;
import de.beckhoff.jni.tcads.AmsAddr;
import de.beckhoff.jni.tcads.AdsCallDllFunction;

public class Main
{
    public static void main(String[] args)
    {
    long err;
    AmsAddr addr = new AmsAddr();
    JNIByteBuffer handleBuff = new JNIByteBuffer(Integer.SIZE / Byte.SIZE);
    JNIByteBuffer symbolBuff = new JNIByteBuffer(
        Convert.StringToByteArr("MAIN.PLCVar",true));
    JNIByteBuffer dataBuff = new JNIByteBuffer(Integer.SIZE / Byte.SIZE);
        
    // Open communication        
    AdsCallDllFunction.adsPortOpen();
    err = AdsCallDllFunction.getLocalAddress(addr);
    addr.setPort(AdsCallDllFunction.AMSPORT_R0_PLC_RTS1);

    if (err != 0) {
        System.out.println("Error: Open communication: 0x"
            + Long.toHexString(err));
    } else {
        System.out.println("Success: Open communication!");
    }

    // Get handle by symbol name
    err = AdsCallDllFunction.adsSyncReadWriteReq(addr,
                        AdsCallDllFunction.ADSIGRP_SYM_HNDBYNAME,
                        0x0,
                        handleBuff.getUsedBytesCount(),
                        handleBuff,
                        symbolBuff.getUsedBytesCount(),
                        symbolBuff);
    if(err!=0) { 
        System.out.println("Error: Get handle: 0x" 
            + Long.toHexString(err)); 
    } else {
        System.out.println("Success: Get handle!");
    }

    // Handle: byte[] to int
    int hdlBuffToInt = Convert.ByteArrToInt(handleBuff.getByteArray());
        
    // Read value by handle
    err = AdsCallDllFunction.adsSyncReadReq(addr,
                        AdsCallDllFunction.ADSIGRP_SYM_VALBYHND,
                        hdlBuffToInt,
                        0x4,
                        dataBuff);
    if(err!=0)
    {
        System.out.println("Error: Read by handle: 0x"
                + Long.toHexString(err));
    }
    else
    {
        // Data: byte[] to int
        int intVal = Convert.ByteArrToInt(dataBuff.getByteArray());
        System.out.println("Success: PLCVar value: " + intVal);
    }

    // Release handle
    err = AdsCallDllFunction.adsSyncWriteReq(addr,
        AdsCallDllFunction.ADSIGRP_SYM_RELEASEHND,
        0,
        handleBuff.getUsedBytesCount(),
        handleBuff);

    if(err!=0) {
        System.out.println("Error: Release Handle: 0x"
            + Long.toHexString(err));
    } else {
        System.out.println("Success: Release Handle!");
    }
    
    // Close communication
    err = AdsCallDllFunction.adsPortClose();
    if(err!=0) { 
        System.out.println("Error: Close Communication: 0x" 
            + Long.toHexString(err)); 
    }

    try{
        System.in.read();
    }
    catch (Exception e){
        System.out.println("Error: Close program");
    }
    }
}