尝试使用资源/使用/多种资源 [英] try-with-resources / use / multiple resources

问题描述

我使用的Java-API大量使用Autoclosable-Interface，因此在Java try-with-resources中使用.但是，在Java中，您可以指定

I'm using a Java-API which heavily uses the Autoclosable-Interface and thus in Java try-with-resources. However in Java you can specify

try (res1, res2, res3...) {
  ...
}

我们是否可以使用多个资源?看起来像众所周知的回调地狱:

Do we have a way to use more than one resource? It looks like the well known callback-hell:

val database = Databases.openDatabase(dbFile)

database.use {
  database.createResource(ResourceConfiguration.Builder(resPathName, config).build())

  val resMgr = database.getResourceManager(ResourceManagerConfiguration.Builder(resPathName).build())

  resMgr.use {
    val wtx = resMgr.beginNodeWriteTrx()

    wtx.use {
      wtx.insertSubtreeAsFirstChild(XMLShredder.createStringReader(resFileToStore))
    }
  }
}

推荐答案

为简单起见，我将A，B和C用作链式自动闭合装置.

import java.io.Closeable

open class MockCloseable: Closeable {
    override fun close() = TODO("Just for compilation")
}
class A: MockCloseable(){
    fun makeB(): B = TODO()
}
class B: MockCloseable(){
    fun makeC(): C = TODO()

}
class C: MockCloseable()

使用用途

这看起来像这样:

Using uses

This would look like this:

A().use {a ->
    a.makeB().use {b -> 
        b.makeC().use {c -> 
            println(c)
        }
    }
}

通过包装器使链使用功能

定义

class ChainedCloseable<T: Closeable>(val payload: T, val parents: List<Closeable>) {
    fun <U> use(block: (T)->U): U {
        try {
            return block(payload)
        } finally {
            payload.close()
            parents.asReversed().forEach { it.close() }
        }
    }

    fun <U: Closeable> convert(block: (T)->U): ChainedCloseable<U> {
        val newPayload = block(payload)
        return ChainedCloseable(newPayload, parents + payload)
    }
}

fun <T: Closeable, U: Closeable> T.convert(block:(T)->U): ChainedCloseable<U> {
    val new = block(this)

}

用法

A()
    .convert(A::makeB)
    .convert(B::makeC)
    .use { c ->
         println(c)
    }

这使您不必以创建包装对象为代价来避免嵌套太深.

This allows you to avoid having to nest deeply, at the cost of creating wrapper objects.

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