PLC（Programmable Logic Controller）是一种广泛应用于工业自动化领域的自动化控制设备，而Java是一种在计算机科学领域中广泛使用的编程语言。那么，在工业控制领域，如何用Java与PLC互相通信呢？以下是几种Java与PLC通信的方法。

第一种：使用PLC的通信协议

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

第二种：使用OPC（Object Linking and Embedding for Process Control）协议

//连接到OPC服务器
String host = "localhost";
String progId = "OPC.SimaticNET";
JISystem.setAutoRegisterMode(true);
Server server = new Server(host, progId);
server.connect();
//读取PLC数据
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());
//关闭连接
group.clear();
server.dispose();

第三种：使用Modbus TCP协议

//连接到Modbus服务器
InetAddress server = InetAddress.getByName("192.168.0.1");
ModbusTCPTransaction transaction = new ModbusTCPTransaction(server, 502);
TCPMasterConnection connection = new TCPMasterConnection(server);
connection.setPort(502);
connection.connect();
//读取PLC数据
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);
}
//关闭连接
connection.close();

Java与PLC通信的方法有很多，但相应的代码也不尽相同。开发之前应选用适合自己项目的通讯规约，尤其要注意协议端口的设置和数据格式的转换。