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尝试找到可以用更具惯用性的Groovy替换的区域，直到找到{{3}的解决方案}。

我已经开始更深入地研究AST转换注释的使用 - 它们有助于显着减少我在某些地方编写的代码量。但是，我使用groovy.transform.builder.Builder注释与我的一个不可变值类有问题。此批注的来源是托管another issue I've been having。

问题在于注释似乎使构建器直接设置了构建器的值，而不是存储值的副本并将它们传递给构建器的构造函数。当您尝试将其与不可变类一起使用时，这将导致ReadOnlyPropertyException。

您可以使用此注释选择四种可能的构建器策略，其中我已尝试DefaultStrategy，ExternalStrategy和InitializerStrategy。但是，所有这些都造成了问题。

ExternalStrategy看起来是这四个中最有希望的，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()

似乎还有一个相关的JIRA关于此事的讨论here。

修改
我尝试使用InitializerStrategy而非ExternalStrategy使用CFrick的答案。

现在一切都在编译，但是当我尝试执行测试时，我在运行时遇到以下错误：

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)

之后是一系列例外情况，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)

我现在所拥有的是BaseVersion类，如下所示：

/**
 * 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

    // ...
}

生产这些实例的工厂：

/**
 * 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个对象的测试规范类：

/**
 * 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),
        ]

    // ...
}

尝试创建失败的BaseVersion实例的其他类，例如TestSetup。

Answer 1

你的代码失败了，因为那里选择的策略基本上是这样的：

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

，这不能在@Immutable个对象上完成。

根据docs，只有InitializerStrategy，可以明确地处理@Immutable。

您可以将InitializerStrategy与@Canonical和@Immutable结合使用。如果您的@Builder注释没有明确的包含或排除注释属性但@Canonical注释没有，那么来自@Canonical的注释将重新用于@Builder。

E.g。

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)'

根据你的目标，这是一种更糟糕的语法，你可能最好只使用基于地图的c＆＃39; tors。即使没有例如@TypeChecked new Value(vlaue: 666)会产生错误，而留下params（对于具有多个属性的类）会留下null。

有没有办法让@Builder注释适用于不可变类？

1 个答案: