运行Master ireport时，当Master报告中有子报表时，会出现java.lang.NullPointerException

Question

我运行报告的java代码

DBConnector类

public class DBConnector {


private static final String url = "jdbc:postgresql://localhost:5432/DB";
private static final String user = "postgres";
private static final String password = "123"; 

private Connection connection;
private static DBConnector dBConnector = null;

public DBConnector() throws SQLException, ClassNotFoundException {
    connection = null;

    Class.forName("org.postgresql.Driver");
    connection = DriverManager.getConnection(url, user, password);

    if (connection == null) {
        System.out.println("Failed to make connection!");
    }
}

private static DBConnector getDBConnector() throws SQLException, ClassNotFoundException {
    if (dBConnector == null) {
        dBConnector = new DBConnector();
    }
    return dBConnector;
}

public static Connection getConnectionToDB() throws SQLException, ClassNotFoundException {
    return getDBConnector().connection;
}

主报告

主报告中的

参数，此hotelid和custid是我想要发送到子报告的参数 两个参数都是整数

参数属性

主报告中的子报告属性

定义了2个属性

子报告

子报告中的

参数

hotelid properties

在我的子报告中查询

选择名字，姓氏 来自客户 其中custid = $ P {custid}和hotelid = $ P {hotelid}

运行主报告时出现NullPointerException。 我无法找到它的到来。 当我预览报告报告时，生成完美。 有人可以帮帮我???

这是我得到的错误

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at net.sf.jasperreports.engine.JRPropertiesMap.readObject(JRPropertiesMap.java:185)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:974)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1846)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1753)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1945)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1869)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1753)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1667)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1323)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1945)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1869)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1753)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1945)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1869)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1753)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:351)
at net.sf.jasperreports.engine.util.JRLoader.loadObject(JRLoader.java:88)
at net.sf.jasperreports.engine.util.JRLoader.loadObjectFromLocation(JRLoader.java:257)
at net.sf.jasperreports.engine.fill.JRFillSubreport.evaluateSubreport(JRFillSubreport.java:308)
at net.sf.jasperreports.engine.fill.JRFillSubreport.evaluate(JRFillSubreport.java:257)
at net.sf.jasperreports.engine.fill.JRFillElementContainer.evaluate(JRFillElementContainer.java:275)
at net.sf.jasperreports.engine.fill.JRFillBand.evaluate(JRFillBand.java:426)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillBandNoOverflow(JRVerticalFiller.java:424)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillColumnHeader(JRVerticalFiller.java:467)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReportStart(JRVerticalFiller.java:251)
at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReport(JRVerticalFiller.java:113)
at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:891)
at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:795)
at net.sf.jasperreports.engine.fill.JRFiller.fillReport(JRFiller.java:63)
at net.sf.jasperreports.engine.JasperFillManager.fillReport(JasperFillManager.java:402)