PLC（Programmable Logic Controller）是一種廣泛應用于工業自動化領域的自動化控制設備，而Java是一種在計算機科學領域中廣泛使用的編程語言。那么，在工業控制領域，如何用Java與PLC互相通信呢？以下是幾種Java與PLC通信的方法。

第一種：使用PLC的通信協議

Socket socket = new Socket("192.168.0.1", 4001);//連接PLC
OutputStream outputStream = socket.getOutputStream();
InputStream inputStream = socket.getInputStream();
//向PLC發送指令
byte[] cmd = { 0x01, 0x02, 0x03 };
outputStream.write(cmd, 0, cmd.length);
outputStream.flush();
//接收PLC響應
byte[] buffer = new byte[1024];
int len;
while ((len = inputStream.read(buffer)) != -1) {
System.out.println(new String(buffer, 0, len));
}
//關閉連接
inputStream.close();
outputStream.close();
socket.close();

第二種：使用OPC（Object Linking and Embedding for Process Control）協議

//連接到OPC服務器
String host = "localhost";
String progId = "OPC.SimaticNET";
JISystem.setAutoRegisterMode(true);
Server server = new Server(host, progId);
server.connect();
//讀取PLC數據
Group group = server.addGroup("Group");
Item item = group.addItem("Item1", "S7:[S7 connection_1]DB14,DINT20");
item.setActive(true);
OPCItemState itemState = item.read(true);
System.out.println("Value = " + itemState.getValue().getObject());
//關閉連接
group.clear();
server.dispose();

第三種：使用Modbus TCP協議

//連接到Modbus服務器
InetAddress server = InetAddress.getByName("192.168.0.1");
ModbusTCPTransaction transaction = new ModbusTCPTransaction(server, 502);
TCPMasterConnection connection = new TCPMasterConnection(server);
connection.setPort(502);
connection.connect();
//讀取PLC數據
ReadCoilsRequest request = new ReadCoilsRequest(1, 0, 16);
request.setUnitID(1);
transaction.setRequest(request);
transaction.execute();
ReadCoilsResponse response = (ReadCoilsResponse) transaction.getResponse();
boolean[] coils = response.getBooleanData();
for (boolean b : coils) {
System.out.println("Coil: " + b);
}
//關閉連接
connection.close();

Java與PLC通信的方法有很多，但相應的代碼也不盡相同。開發之前應選用適合自己項目的通訊規約，尤其要注意協議端口的設置和數據格式的轉換。