groovy - 有没有办法让 @Builder 注释适用于不可变类？

Question

我正在尝试在 Groovy 中开发一个项目，并且我一直在查看我的代码并试图找到可以用更惯用的 Groovy 替换的区域，直到我找到 another issue I've been having 的解决方案。 .

我已经开始更深入地研究 AST 转换注释的使用 - 它们帮助显着减少了我必须在某些地方编写的代码量。但是，我在使用 groovy.transform.builder.Builder 时遇到了问题使用我的不可变值类之一进行注释。此注释的来源托管 here .

问题是注释似乎使构建器直接设置构建者的值，而不是存储值的副本并将它们传递给构建者的构造函数。这会导致 ReadOnlyPropertyException当您尝试将它与不可变类一起使用时。

您可以使用此注释选择四种可能的 Builder 策略，其中我尝试过 DefaultStrategy , ExternalStrategy和 InitializerStrategy .然而，所有这些都造成了问题。
ExternalStrategy看起来是四个中最有前途的，你可以找到一个基于它的 SSCCE 详细说明问题here .

示例中的源代码也包含在下面:

import groovy.transform.Immutable
import groovy.transform.builder.Builder as GBuilder
import groovy.transform.builder.ExternalStrategy

/*
* Uncommenting the below causes a failure:
* 'groovy.lang.ReadOnlyPropertyException: Cannot set readonly property: value for class: Value'
*/
//@Immutable
class Value {

    @GBuilder(forClass = Value, prefix = 'set', builderStrategy = ExternalStrategy)
    static class Builder { }

    int value
    String toString() { "Value($value)" }
}

def builder = new Value.Builder()
println builder.setValue(1).build()

好像也有相关的JIRA讨论 here .

编辑
我尝试使用下面的 CFrick 答案，使用 InitializerStrategy而不是 ExternalStrategy .

现在一切都可以编译了，但是当我尝试执行测试时，在运行时出现以下错误:

java.lang.IllegalAccessError: tried to access class com.github.tagc.semver.version.BaseVersion from class com.github.tagc.semver.version.BaseVersion$com.github.tagc.semver.version.BaseVersionInitializer
    at java.lang.Class.getDeclaringClass(Class.java:1227)
    at java.beans.MethodRef.set(MethodRef.java:46)
    at java.beans.MethodDescriptor.setMethod(MethodDescriptor.java:117)
    at java.beans.MethodDescriptor.<init>(MethodDescriptor.java:72)
    at java.beans.MethodDescriptor.<init>(MethodDescriptor.java:56)
    at java.beans.Introspector.getTargetMethodInfo(Introspector.java:1163)
    at java.beans.Introspector.getBeanInfo(Introspector.java:426)
    at java.beans.Introspector.getBeanInfo(Introspector.java:173)
    at com.github.tagc.semver.version.VersionFactory.createBaseVersion(VersionFactory.groovy:34)
    at com.github.tagc.semver.test.util.TestSetup.<clinit>(TestSetup.groovy:77)
    at java.lang.Class.forName(Class.java:344)
    at com.github.tagc.semver.version.SnapshotDecoratorSpec.#decoratedVersion should be considered equal to patch-bumped #releaseVersion snapshot(SnapshotDecoratorSpec.groovy:24)

之后是一系列异常，如下所示:

java.lang.NoClassDefFoundError: Could not initialize class com.github.tagc.semver.test.util.TestSetup
    at java.lang.Class.forName(Class.java:344)
    at com.github.tagc.semver.version.SnapshotDecoratorSpec.#decoratedVersion should be considered equal to minor-bumped #releaseVersion snapshot(SnapshotDecoratorSpec.groovy:36)

我现在拥有的是 BaseVersion类如下:

/**
 * A concrete, base implementation of {@link com.github.tagc.semver.version.Version Version}.
 *
 * @author davidfallah
 * @since v0.1.0
 */
@Immutable
@Builder(prefix = 'set', builderStrategy = InitializerStrategy)
@PackageScope
final class BaseVersion implements Version {
    // ...

    /**
     * The major category of this version.
     */
    int major = 0

    /**
     * The minor category of this version.
     */
    int minor = 0

    /**
     * The patch category of this version.
     */
    int patch = 0

    /**
     * Whether this version is a release or snapshot version.
     */
    boolean release = false

    // ...
}

生产以下实例的工厂:

/**
 * A factory for producing base and decorated {@code Version} objects.
 *
 * @author davidfallah
 * @since v0.5.0
 */
class VersionFactory {

    // ...

    /**
     * Returns an instance of {@link com.github.tagc.semver.version.BaseVersion BaseVersion} constructed
     * with the given parameters.
     *
     * @param major the major category value of the version instance
     * @param minor the minor category value of the version instance
     * @param patch the patch category value of the version instance
     * @param release the release setting of the version instance
     * @return an instance of {@code BaseVersion}
     */
    static BaseVersion createBaseVersion(int major, int minor, int patch, boolean release) {
        return new BaseVersion(major, minor, patch, release)
    }

    /**
     * Returns an instance of {@link com.github.tagc.semver.version.BaseVersion BaseVersion} constructed
     * with the given parameters.
     *
     * @param m a map of parameter names and their corresponding values corresponding to the
     *        construction parameters of {@code BaseVersion}.
     *
     * @return an instance of {@code BaseVersion}
     */
    static BaseVersion createBaseVersion(Map m) {
        return new BaseVersion(m)
    }

    /**
     * Returns an instance of {@link com.github.tagc.semver.version.BaseVersion BaseVersion} constructed
     * with the given parameters.
     *
     * @param l a list of parameter values corresponding to the construction parameters of {@code BaseVersion}.
     *
     * @return an instance of {@code BaseVersion}
     */
    static BaseVersion createBaseVersion(List l) {
        return new BaseVersion(l)
    }

    /**
     * Returns a builder for {@link com.github.tagc.semver.version.BaseVersion BaseVersion} to specify
     * the construction parameters for the {@code BaseVersion} incrementally.
     *
     * @return an instance of {@code BaseVersion.Builder}
     */
    static Object createBaseVersionBuilder() {
        return BaseVersion.builder()
    }

    // ...
}

Version 的测试规范类对象:

/**
 * Test specification for {@link com.github.tagc.semver.version.Version Version}.
 *
 * @author davidfallah
 * @since 0.1.0
 */
@Unroll
class VersionSpec extends Specification {

    static exampleVersions = [
        VersionFactory.createBaseVersion(major:1, minor:2, patch:3),
        VersionFactory.createBaseVersion(major:0, minor:0, patch:0),
        VersionFactory.createBaseVersion(major:5, minor:4, patch:3),
        VersionFactory.createBaseVersion(major:1, minor:16, patch:2),
        VersionFactory.createBaseVersion(major:4, minor:5, patch:8),
        ]

    // ...
}

以及其他尝试创建 BaseVersion 实例的类失败的，例如 TestSetup .

Answer 1

你那里的代码失败了，因为那里选择的策略基本上是:

 def v = new Value().with{ setValue(1); return it }

这不能在 @Immutable 上完成对象。

根据 docs ，只有 InitializerStrategy ，可以明确应对 @Immutable .

You can use the InitializerStrategy in conjunction with @Canonical and @Immutable. If your @Builder annotation doesn’t have explicit includes or excludes annotation attributes but your @Canonical annotation does, the ones from @Canonical will be re-used for @Builder.

例如。

import groovy.transform.*
import groovy.transform.builder.*

@Immutable
@ToString
@Builder(prefix='set', builderStrategy=InitializerStrategy)
class Value {
    int value
}

def builder = Value.createInitializer().setValue(1)
assert new Value(builder).toString()=='Value(1)'

取决于你在做什么，这是非常丑陋的语法，你最好只使用基于 Map 的 c'tors。即使没有例如 @TypeChecked new Value(vlaue: 666)将产生一个错误并留下参数(对于具有多个属性的类)将留下它们 null .