有沒有辦法讓@Builder註釋適用於不可變類？

Question

我正試圖在Groovy中開發一個項目，並且一直在尋找我的代碼並試圖找到可以用更通俗的Groovy替換的區域，直到找到another issue I've been having的解決方案。

我已經開始更深入地研究AST轉換註釋的使用 - 它們幫助大幅減少了我在某些地方編寫的代碼量。不過，我有一個問題，使用groovy.transform.builder.Builder註釋與我的一個不可變的值類。此註釋的來源託管於here。

問題是，註釋似乎使構建器直接設置buildee的值，而不是存儲值的副本並將它們傳遞給buildee的構造函數。當您嘗試將其與不可變類一起使用時，會導致ReadOnlyPropertyException。

有四種可能的構建器策略，您可以選擇這個註釋，其中我試過DefaultStrategy,ExternalStrategy和InitializerStrategy。但是，所有這些都造成了問題。

ExternalStrategy看起來像四個最有前途的，你可以找到一個SSCCE的基礎上詳細說明問題here。

從示例的源代碼也包括在下面：

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() 

看起來也似乎是對此事here相關的JIRA討論。

編輯
我用下面CFrick的答案試過，使用InitializerStrategy而非ExternalStrategy。

現在一切編譯，但我會在運行時下面的錯誤，當我嘗試執行我的測試：

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) 

：

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) 

通過類似下面的一系列異常此後其次

我現在所擁有的是一個BaseVersion類像下面這樣：

/** 
* 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 

    // ... 
} 

一家工廠，生產的這些實例：

/** 
* 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() 
    } 

    // ... 
} 

爲Version對象的測試規範類：

/** 
* 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), 
     ] 

    // ... 
} 

和其它類，嘗試創建是失敗的BaseVersion情況下，如TestSetup。

Answer 1

你的代碼中有失敗，因爲選擇的策略有基本的作用：

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

，這不能@Immutable對象來完成。

根據docs，只有InitializerStrategy，可以明確應對@Immutable。

您可以將InitializerStrategy與@Canonical和@Immutable結合使用。如果您的@Builder註釋沒有顯式包含或排除註釋屬性，但您的@Canonical註釋確實會這樣做，@Canonical的註釋屬性將被重用於@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)' 

這取決於你的行爲，這是更醜陋的語法，你可能會更好使用基於地圖的c'tors。即使沒有例如@TypeChecked a new Value(vlaue: 666)將產生一個錯誤，並留下參數（對於具有多個屬性的類）將使它們保留null。