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PORefactoring and removing if null checks in chain filtering
 

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    <p>I'm doing some filtering on database entries and I ended up with somewhat ugly code, which I don't like.</p> <p>I have my <code>MyFilterResolverFactory</code> class where I build and return my <code>MyFilterResolver</code> chain.</p> <pre><code>public abstract class MyFilterResolver { protected MyFilterResolver nextResolver = EMPTY; protected List&lt;Predicate&gt; predicates; public List&lt;Predicate&gt; resolve(MyFilter filter, CriteriaBuilder cb, Root&lt;MyEntity&gt; root) { this.predicates = new ArrayList&lt;Predicate&gt;(); resolveFilter(filter, cb, root); this.predicates.addAll(this.nextResolver.resolve(filter, cb, root)); return this.predicates; } protected abstract void resolveFilter(MyFilter filter, CriteriaBuilder cb, Root&lt;MyEntity&gt; root); public void attachNextResolver(MyFilterResolver nextResolver) { this.nextResolver = nextResolver; } public static MyFilterResolver EMPTY = new MyFilterResolver() { @Override public List&lt;Predicate&gt; resolve(MyFilter filter, CriteriaBuilder cb, Root&lt;MyEntity&gt; root) { return new ArrayList&lt;Predicate&gt;(); } @Override protected void resolveFilter(MyFilter filter, CriteriaBuilder cb, Root&lt;MyEntity&gt; root) { } }; } </code></pre> <p>And an ugly, concrete implementation of it:</p> <pre><code>public class MyDateFilterResolver extends MyFilterResolver { @Override protected void resolveFilter(MyFilter filter, CriteriaBuilder cb, Root&lt;MyEntity&gt; root) { if (filter != null) { Date dateExact = filter.getDateExact(); Date dateAfter = filter.getDateAfter(); Date dateBefore = filter.getDateBefore(); if (dateExact != null) { Calendar calendar = Calendar.getInstance(); calendar.setTime(dateExact); calendar.set(Calendar.HOUR_OF_DAY, 0); calendar.set(Calendar.MINUTE, 0); calendar.set(Calendar.SECOND, 0); calendar.set(Calendar.MILLISECOND, 0); Date dayStart = calendar.getTime(); calendar = Calendar.getInstance(); calendar.setTime(dayStart); calendar.add(Calendar.DATE, 1); calendar.add(Calendar.MILLISECOND, -1); Date dayEnd = calendar.getTime(); super.predicates.add( cb.greaterThanOrEqualTo( root.get("date").as(Date.class), dayStart ) ); super.predicates.add( cb.lessThanOrEqualTo( root.get("date").as(Date.class), dayEnd ) ); } if (dateAfter != null) { super.predicates.add( cb.greaterThanOrEqualTo( root.get("date").as(Date.class), dateAfter ) ); } if (dateBefore != null) { predicates.add( cb.lessThanOrEqualTo( root.get("date").as(Date.class), dateBefore ) ); } } } } </code></pre> <p><code>MyFilter</code> class is a regular POJO with getters/setters only.</p> <p>I'd like to get rid of these <code>if (something != null)</code> checks, but I am not able to see how.</p>
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