我正在尝试将一分钟内收到的所有消息对象存储到树形图中,一分钟结束后,将其序列化并将字节 [] 返回到另一个类,同时清除地图并开始存储下一分钟收到的消息等上。
public class StoreMessage extends Thread implements Serializable{
public static byte[] b=null;
public static Map <Long,Message> map1=Collections.synchronizedMap(new TreeMap<Long,Message>());
public static Calendar c1=Calendar.getInstance();
public static int year=c1.get(Calendar.YEAR);
public static int month=c1.get(Calendar.MONTH);
public static int day=c1.get(Calendar.DAY_OF_MONTH);
public static int hour=c1.get(Calendar.HOUR_OF_DAY);
public static int min=c1.get(Calendar.MINUTE);
public static GregorianCalendar gc = new GregorianCalendar(year, month, day, hour, min);
public static Date d=gc.getTime();
public static long time1=(d.getTime())/60000; //precision till minute of the time elapsed since 1 Jan 1970
public static long time2=time1+1;
public static byte[] store(Message message)throws Exception{
while(true)
{
if(time1<time2)
{
long preciseTime=TimeUnit.MILLISECONDS.toNanos(System.currentTimeMillis())+(System.nanoTime()-startNanotime);
map1.put(preciseTime, message);
}
else
{
b=Serializer.serialize(map1);
map1.clear();
time1=time2;
time2++;
return b;
}
}
}
}
为什么这段代码给我空指针异常突出显示 int len=b.length; 调用它返回值的另一个类?
public static void record(Message message){
try{
//storing the serialized message in byte[]
byte[] b =StoreMessage.store(message);
int len=b.length; //<--highlights this line for null pointer exception
即使在进行了修改(即,将 return 放在 else 块中)之后,它也不会将控制权返回给调用类。此外,在 else 块内没有打印任何SOP语句(添加时)。为什么?
The Serializer class
public class Serializer {
//serializes an object and returns a byte array
public static byte[] serialize(Object map) throws IOException
{
ByteArrayOutputStream b = new ByteArrayOutputStream();
ObjectOutputStream o = new ObjectOutputStream(b);
o.writeObject(map);
return b.toByteArray();
}
//de-serialization of the byte array and returns an object
public static Object toObject (byte[] bytes)
{
Object obj = null;
try
{
ByteArrayInputStream bis = new ByteArrayInputStream (bytes);
ObjectInputStream ois = new ObjectInputStream (bis);
obj = ois.readObject();
}
catch (Exception ex) { }
return obj;
}
}