用Java将int转换为long

Question

This questions has many answers and I have seen them. I have code that has been working but today suddenly it starting throwing java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Long for the line

return null == input.get(keyName) ? 0L : (long) input.get(keyName);

Error is coming from (long) input.get(keyName) . I wonder why it starting breaking all of sudden. (long) input.get(keyName) this looks good to me. I thought of doing ((Integer) input.get(keyName)).longValue() but was getting java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.Integer as map sometimes contains long values. Any suggestions

Stacktrace:

java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Long
    at accountservice.adapter.batch.testJob.SyncDriverPartitioner.getLongValueFromMap(SyncDriverPartitioner.java:78) ~[classes/:?]
    at accountservice.adapter.batch.testJob.SyncDriverPartitioner.partition(SyncDriverPartitioner.java:47) ~[classes/:?]
    at accountservice.adapter.batch.testJob.SyncDriverPartitioner$$FastClassBySpringCGLIB$$6f3315e4.invoke(<generated>) ~[classes/:?]
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) ~[spring-core-4.3.18.RELEASE.jar:4.3.18.RELEASE]

Answer 1

You can take advantage of the fact that all numeric primitive wrappers extend java.lang.Number :

return null == input.get(keyName) ? 0L : ((Number) input.get(keyName)).longValue();

As to why it started giving errors suddenly; really the only likely reason is that up until it started failing, you were always putting java.lang.Long objects in the input Map, and it changed so you're also putting java.lang.Integer in them now.

It's quite easy for that to happen with auto-boxing and numeric constants:

long v = 42;
input.put("key", v);  // Puts a java.lang.Long in the map
input.put("key", 42); // Puts a java.lang.Integer in the map
input.put("key", 42L); // Puts a java.lang.Long in the map

You can avoid it by declare your Map type-safely ( Map<String, Long> ). If you do that, input.put("key", 42) will give a compile-time error.

Answer 2

Rather than casting an int to a long I would suggest:

return null == input.get(keyName) ? 0L : Integer.toUnsignedLong(input.get(keyName))

At least this way you should get some more information about why it cannot be converted to a long rather than just a ClassCastException

Answer Update

Based on your comments I guess you are going to have to check type of the entry in Map before processing it, I would suggest the following:

    Object keyValue = input.get(keyName);
    if (null == keyValue) return 0L;
    String valueType = keyValue.getClass().getTypeName();
    if (valueType.equals(Long.class.getTypeName())) {
        return (long) keyValue;
    }
    if (valueType.equals(Integer.class.getTypeName())) {
        return Integer.toUnsignedLong((int) keyValue);
    }
    throw new TypeMismatchException(String.format("Type '%s' is not supported...", valueType));

This will let you define different operations for different types of entry, it is extendable to any types you want to support. You can tweak the exception thrown as well to provide you relevant information.

The snippet above shows you the actual type so that you can extend your code to support that type, or work out why something of that type got into your map.

It should be noted that it would probably be better to do this when data is entered into the map, not when it's taken out of the map. In which case you should be able to change your map to a type . It's always better to sanitise your imputes than trying to deal with a mishmash of mixed data types at a later date.