Develop Reference

PMD reference to a mutable object of an interface

Similar to this question. I have an interface DateRangeModel:
I use this to automatically validate dates in implementers:
public interface DateRangeModel {
#ApiModelProperty(value = "From date. Must be less than to date.")
#Column()
Date getFromDate();
void setFromDate(Date date);
#ApiModelProperty(value = "To date. Must be greater than to date.")
#Column()
Date getToDate();
void setToDate(Date date);
/**
* Checks that if both dates are populated, a valid date range is used.
*
* #return true if the date is a valid range.
*/
#AssertTrue(message = "To date must be greater than or equal to from date.")
#JsonIgnore
default boolean areDatesValid() {
if (getToDate() != null && getFromDate() != null) {
return !getFromDate().after(getToDate());
}
return true;
}
}
I implement it like this:
#EqualsAndHashCode
#Data
#Builder
public class BirthdayParty implements DateRangeModel {
Date fromDate;
Date toDate;
String name;
}
Which compiles and seems to work, but I get that error when running PMD:
Returning a reference to a mutable object value stored in one of the object's fields exposes the internal representation of the object.
How can I either accomplish what I want (an interface with to/from date validation) without having to implement the setDate methods in all implementers (which I think would defeat the purpose)?

The problem is that java.util.Date is mutable and you return it in your getters. So someone could do this:
BirthdayParty party = ...;
Date fromDate = party.getFromDate();
...
Date someDate = fromDate;
...
// you might not be aware that this also changes the fromDate in party
someDate.setTime(12345678);
There are four things you can do:
Disable the PMD rule.
Suppress the warning everywhere you use one of these a classes.
Don't use Lombok and copy the dates in your setters and getters instead of just storing/returning the reference to a date.
Use java.time.ZonedDateTime (or LocalDateTime) instead of Date. ZonedDateTime is immutable and should not lead to this warning.
I suggest the fourth option. Not only because it gets rid of the PMD warning but also because the new time API in Java 8 is so much better and easier to use than java.util.Date.

Mapping from java.time.MonthDay to java.sql.*

We have a case, where we require only the day and the month and thus would use the java.time.MonthDay (Javadocs) to represent that information.
We are aware that we could create our own JPA object for persistence or just use the java.sql.Date object, but that generally requires an unrequired year information.
Another way is to call the method .atYear(int) (Javadoc) (with a fictitious year) on it and receive a java.time.LocalDate (Javadoc), which can be easily converted to java.sql.Date. But this is prone to missunderstandings in the future (and also persist the year information).
Is there some "elegant"/supposed solution for this case? Or is there a replacement for SQL that supports the whole new date and time API for Persistence.
Another case would be java.time.YearMonth (Javadoc).
Thanks for reading!

Since SQL databases don't have a type compatible with MonthDay, use a VARCHAR columns, and simply use toString() and MonthDay.parse().
Or use a custom DateTimeFormatter, if you don't like the --12-03 format.
The default format will correctly sort, as a string.

here are the code snippets:
// column define:
#Column(name = "date", columnDefinition = "mediumint", nullable = false)
#Convert(converter = MonthDayIntegerAttributeConverter.class)
protected MonthDay date;
// converter define:
public class MonthDayIntegerAttributeConverter implements AttributeConverter<MonthDay, Integer> {
#Override
public Integer convertToDatabaseColumn(MonthDay attribute) {
return (attribute.getMonthValue() * 100) + attribute.getDayOfMonth();
}
#Override
public MonthDay convertToEntityAttribute(Integer dbData) {
int month = dbData / 100;
int day = dbData % 100;
return MonthDay.of(month, day);
}
}

How to persist Joda Date to sql database?

How can I persist a jodatime YearMonth object to a sql database?
#Entity
public class MyEntity {
private YearMonth date; //how to persist?
//some more properties
}
I want later to be able to pick all entities by a specific month.

The better question is how do you intend to use the data in the database? Generally you want to store dates in databases using data types supported by the target database as opposed to strings or composite integers. That would allow you to use the built in database date/time functions and validations as opposed to needing to implement that logic in your application.
You can certainly add methods to your entity to convert to/from jodatime values to your entity for the parts of your application that need it.

You need a javax.persistence.Converter for this (see How to convert java.util.Date to Java8 java.time.YearMonth):
#Entity
public class MyEntity {
#Convert(converter = YearMonthConverter.class)
private YearMonth date; //how to persist?
//some more properties
}
The following is an example converter for Java8 java.time.YearMonth to java.utilDate. You need to change java.time.YearMonth to org.joda.time.YearMonth and use the appropriate methods to convert to/from the desired type:
(imports omitted):
#Converter(autoApply = true)
public class YearMonthConverter implements AttributeConverter<YearMonth, Date> {
#Override
public Date convertToDatabaseColumn(YearMonth attribute) {
// uses default zone since in the end only dates are needed
return attribute == null ? null : Date.from(attribute.atDay(1).atStartOfDay(ZoneId.systemDefault()).toInstant());
}
#Override
public YearMonth convertToEntityAttribute(Date dbData) {
// TODO: check if Date -> YearMonth can't be done in a better way
if (dbData == null) return null;
Calendar calendar = Calendar.getInstance();
calendar.setTime(dbData);
return YearMonth.of(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH) + 1);
}
}

cast date to ms to add long value of duration with criteria

I have a date and duration. I need to add the duration to date. Date's format is timestamp, duration's - Long (milliseconds). How can I wright criteria to deal this issue?
Practically i have something like this:
03-17-2014 21:24:57 + 2523566;

If you want to do it in Java and have a java.sql.Date and a long:
public java.sql.Date dateAdd(java.sql.Date inputDate, long duration)
{
return new java.sql.Date(inputDate.getTime() + duration);
}
A java.sql.Timestamp can be used in place of a java.sql.Date in either the argument or the return value, if required.

How do I use a comparator (for a binary search) to compare a DateTime to a DateTime field in an object?

I want to compare inputted dates to a sorted list of holidays objects using a binary search. The holiday objects consist of a string with the name and a jodatime Datetime. So I am comparing the same types but one is part of an object and the other is not.
I have:
public class DateTimeComparator implements Comparator<DateTime> {
public int compare(DateTime userDate, DateTime listHoliday) {
if (userDate.equals(Holidays.getAllHolidays().date)) {
return 1;
}
else {
return 0;
}
}
}
Eclipse's feedback is that date can't be resolved. How can I correctly point to the date field of my Holiday list?
Edit: So if I don't need a comparator (suggested to me in another question), how do I structure my binary search? So far I have:
public static boolean isHoliday(List<Holiday> holidayList, DateTime date) {
if(Collections.binarySearch(holidayList.date, date)) {
return true;
}
return false;
}

You don't need to write a Comparator for this, DateTimes are already inherently Comparable. Also, referencing the date field for a LIST is non-sensical; its the ELEMENTS of the list with have that field, not the list itself.
You want to use Collections.binarySearch instead, and handle the output yourself.

I solved this by creating a new holiday and comparing two holiday objects to each other with a comparator that looks at the DateTime field.