问题
My code currently works something similar to this
public void foo (Statement st, String sqlStr, String tempTableName) {
String aString = foo(tempTableName);
boolean result = st.execute(aString); // creates temp table
// Now do something else in another method
writeToTT(st, tempTableName);
}
public void writeToTT(Statement st, String tempTableName) {
// Final String name
String finalSqlWithTempTableName = foo(tempTableName);
st.execute(finalSqlWithTempTableName);
}
The above works fine. However, when I pass the Statement object as part of a HashMap it fails inside the writeToTT method
public void foo (Statement st, String sqlStr, String tempTableName) {
String aString = foo(tempTableName);
st.exectue(aString); // Creates temp table
// Now do something else in another method but pass it within a map
Map<String,Object> mapObj = new HashMap<>();
mapObj.put("statement",st);
writeToTT(mapObj, tempTableName);
}
public void writeToTT(Map<String,Object> mapObj, String tempTableName) {
// Final String name
String finalSqlWithTempTableName = foo(tempTableName);
Statement st = (Statement)mapObj.get("statement");
st.execute(finalSqlWithTempTableName); // Fails here saying that tempTableName object doesn't exist.
}
I used a debugger to check the identity Hash Code using System.identityHashCode(obj) - and both cases (inside and outside the method frame stack) the hash codes are the same. It's indeed referring to the same object using the reference value passed in paramMap.
I am just trying to understand whether this is because how it's being passed as a new object reference with HashMap or is it because the actual statement object doesn't have a valid hashCode override?
My assumption/understanding is that the temp table location in memory and the Statement object's access to that memory location changes as soon as I pass it via HashMap even though the object hashCode remains the same within writeToTT method. But may be I am mistaken?
来源：https://stackoverflow.com/questions/57380797/cannot-reach-a-temp-table-using-java-sql-statement-object-passed-as-a-map-value