要調用網絡打印機，可以使用Java中的javax.print包來實現。以下是一個簡單的示例代碼，演示如何在Java中調用網絡打印機：

import javax.print.*;
import javax.print.attribute.HashPrintRequestAttributeSet;
import javax.print.attribute.PrintRequestAttributeSet;
import javax.print.attribute.standard.Copies;
import javax.print.attribute.standard.PrinterName;

public class NetworkPrinterExample {

    public static void main(String[] args) {
        // 指定網絡打印機的IP地址或主機名
        String printerIP = "192.168.1.100";
        
        // 創建打印服務
        PrintService[] services = PrintServiceLookup.lookupPrintServices(null, null);
        
        // 查找指定名稱的打印機
        PrintService networkPrinter = null;
        for (PrintService service : services) {
            if (service.getName().equals(printerIP)) {
                networkPrinter = service;
                break;
            }
        }
        
        if (networkPrinter != null) {
            // 創建打印請求屬性集
            PrintRequestAttributeSet attributes = new HashPrintRequestAttributeSet();
            attributes.add(new Copies(1)); // 設置打印份數
            
            // 打印文檔
            try {
                DocPrintJob printJob = networkPrinter.createPrintJob();
                Doc doc = new SimpleDoc("Hello, World".getBytes(), DocFlavor.BYTE_ARRAY.AUTOSENSE, null);
                printJob.print(doc, attributes);
            } catch (PrintException e) {
                e.printStackTrace();
            }
        } else {
            System.out.println("Network printer not found.");
        }
    }
}

請注意，上述示例代碼中的printerIP變量應該設置為您要連接的網絡打印機的IP地址或主機名。通過查找與指定名稱匹配的打印機服務，然后創建打印請求屬性集并打印文檔，即可實現調用網絡打印機。