Path: csiph.com!eternal-september.org!feeder.eternal-september.org!reader01.eternal-september.org!.POSTED!not-for-mail
From: Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: Does this make sense?
Date: Sun, 7 Apr 2019 22:14:51 +0200
Organization: A noiseless patient Spider
Lines: 64
Message-ID: <q8dloh$fh9$1@dont-email.me>
References: <f9818c55-5eb6-47f8-8ec9-d512861ddee7@googlegroups.com> <q84vam$lri$1@dont-email.me> <c001151d-044c-4d1b-ad88-0efd923e4433@googlegroups.com> <q85699$oq6$1@dont-email.me> <b8961ec3-eac5-45da-aa5d-11144bcae219@googlegroups.com> <q87t34$l7l$1@newsreader4.netcologne.de>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Injection-Date: Sun, 7 Apr 2019 20:15:14 -0000 (UTC)
Injection-Info: reader02.eternal-september.org; posting-host="acb4316d6da48adbd4d1afd1346ee54f"; logging-data="15913"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX18XE7C88x4poMHRZ/5HSQrj"
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1
Cancel-Lock: sha1:NU+wy/EP6De5mMycLYC44yVC3do=
In-Reply-To: <q87t34$l7l$1@newsreader4.netcologne.de>
X-Antivirus-Status: Clean
Content-Language: en-US
X-Antivirus: AVG (VPS 190407-4, 04/07/2019), Outbound message
Xref: csiph.com comp.lang.java.programmer:38879

> Assume you implement the following:
> 
> @FunctionalInterface
> public interface CheckedFunction<I, O, E extends Exception> {
>   O apply(I input) throws E;
> }
> 
> @FunctionalInterface
> public interface CheckedSupplier<O, E extends Exception> {
>   O get() throws E;
> }
> 
> public static <I, O, E extends Exception> O tryAlternatives(
>     CheckedFunction<I, O, E> op,
>     I firstInput,
>     I... moreInputs
> ) throws E { ... }
> 
> public class CumulativeResource<T extends AutoCloseable>
>     implements AutoCloseable {
>   public final T resource;
> 
>   public interface CumulativeResourceBuilder<T extends AutoCloseable> {
>     <S extends AutoCloseable> CumulativeResourceBuilder<S>
>       cumulate(CheckedFunction<T, S, Exception> builder);
>     CumulativeResource<T> build() throws Exception;
>   }
> 
>   public static <T extends AutoCloseable> CumulativeResourceBuilder<T>
>     from(CheckedSupplier<T, Exception> factory) { ... }
> }
> 
> Then your actual code might become this:
> 
> CumulativeResource<ResultSet> fetchResult(String dbUrl)
>     throws Exception {
>   return
>     CumulativeResource
>       .from(() -> DriverManager.getConnection(dbUrl, user, password))
>       .cumulate(c ->
>         c.prepareStatement(
>           query,
>           ResultSet.TYPE_SCROLL_INSENSITIVE,
>           ResultSet.CONCUR_READ_ONLY
>         )
>       )
>       .cumulate(PreparedStatement::executeQuery)
>       .build();
>     }
> 
> void runQuery() throws Exception {
>   try(CumulativeResource<ResultSet> rsRes =
>       tryAlternatives(this::fetchResult, firstDbUrl, secondDbUrl)) {
>     ResultSet rs = rsRes.resource;
>     while (rs.next()) {
>       System.out.println(rs.getRow());
>     }
>   }
> }

Sexy.

-- 
DF.