java.lang.NullPointerException at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1009)

Question

       java.lang.NullPointerException
       at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1009)
       at java.lang.Float.parseFloat(Float.java:439)
       at ConvertReadings.Convertd(ConvertReadings.java:39)
       at UDPServer.main(UDPServer.java:73)

休眠配置文件

<hibernate-configuration>
             <session-factory>

        <property name="connection.driver_class">
            com.mysql.jdbc.Driver</property>
        <property name="connection.url">
        jdbc:mysql://localhost:1111/DB</property>
        <property name="connection.username">username</property>
        <property name="connection.password">password</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="connection.autoReconnect"> true</property>
            <property name="connection.autoReconnectForPools">true</property>
        <!--  <property name="c3p0.validate">true</property> -->
            <property name="current_session_context_class">thread</property>
            <property name="hibernate.format_sql">false</property>
            <property name="hibernate.connection.pool_size">5</property> 
            <property name="hibernate.c3p0.acquire_increment">1</property> 
        <property name="hibernate.c3p0.idle_test_period">1000</property> 
        <property name="hibernate.c3p0.max_size">5</property> 
        <property name="hibernate.c3p0.max_statements">0</property> 
        <property name="hibernate.c3p0.min_size">3</property> 
        <property name="hibernate.c3p0.timeout">5000</property>

ConvertReadings 代码是

public class ConvertReadings {
public String Convertd(String a, String b, String c1, String c0 ) throws Exception
{
    Converter con= new Converter();
    int x;
    double i = Float.parseFloat(a);
    if (b.equalsIgnoreCase("HUM"))
    {
        double c=Float.parseFloat(c1);
        double d=Float.parseFloat(c0);
        x=con.convert(c, d, i);
        return String.valueOf(x);
    }
    else if (b.equalsIgnoreCase("CO"))
    {
        double c=Float.parseFloat(c1);;
        double d=Float.parseFloat(c0);
        x=con.convert(c, d, i);
        return String.valueOf(x);
}
    return "Invalid sensor reading";
}
}

我遇到异常的代码是

import java.util.Iterator;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.SessionFactory;
import org.hibernate.classic.Session;
public class FetchCoeff {
public SessionFactory factory;
public String[] testing(String x, String y) { ///here x=DevID and y= sensor type
//Session session= null ;
String c[] = new String[30];
Session session = factory.openSession(); 
    try{
String q= "SELECT d.c1, d.c0, d.DevID, d.SensorType FROM SensorReadings d WHERE d.DevID= :DevID AND d.SensorType= :SensorType";
Query query = session.createQuery(q);
query.setParameter("DevID",x);
query.setParameter("SensorType", y);
System.out.println("query executed");
for(Iterator it=query.iterate();it.hasNext();){
      Object[] ob = (Object[]) it.next();       // I am Facing problem here
        c[1]= (String)ob[0];  // contains coeff 1 c1
        c[0]= (String)ob[1];  // contains coeff 0 c0    
     }
}catch(HibernateException e){
    System.out.println("Hibernate exception occured");
    e.printStackTrace();
}catch(Exception d){
    System.out.println("exception occured");
    d.printStackTrace();
}
finally
{
session.close();
}
return c;
}
}

几周前我已经发布了它，我从“JB Nizet”那里得到了解决方案，但它只解决了一部分，现在我在下面的部分面临空指针异常

                for(Iterator it=query.iterate();it.hasNext();){
             Object[] ob = (Object[]) it.next();
                c[1]= (String)ob[0];
                c[0]= (String)ob[1];

我认为这个对象正在抛出空指针异常，但我不知道如何解决它。任何人都可以在这方面帮助我.. 在这里我创建了查询和迭代结果集并将其传递给字符串数组。

Answer 1

如果我理解正确，您多次执行上述方法，并且在一些调用之后，它会抛出上述异常。

问题可能来自这样一个事实，即您正在阅读 Hibernate 配置并在每次方法调用时创建一个全新的会话工厂和一个新的连接池。

以下内容应该只做一次。然后应该在每次方法调用时重用相同的会话工厂：

Configuration cfg= new Configuration();
cfg.configure("Hibernate.cfg.xml");
SessionFactory sessionfactory = cfg.buildSessionFactory();