java - 是否可以使用 Gradle 5 为 Java 6 编译和测试 Groovy 源文件？

Question

根据客户要求，我目前使用的是 Java 6，因此我现在使用的是 Gradle 2.14.1。为了能够将 Gradle 升级到最新版本并仍然针对 Java 6 进行编译和测试，我遵循了官方用户指南中的说明 - 请参阅 Groovy Cross Compilation .

从我的角度来看，使用上述配置，编译以下示例 Groovy 类应该会导致错误，因为它使用了 Java 8 中引入的类。

import groovy.transform.TypeChecked

@TypeChecked
class SomeGroovyClass {
    Optional<String> someGroovyMethod() {
        return Optional.empty()
    }
}

但是 Gradle 构建以某种方式成功了。我在这里错过了什么吗？如何使用最新的 Gradle 版本并仍然编译和测试 Java 6 的 Groovy 源文件和 Java 源文件？

如果我将上述类转换为 Java 类，构建会像预期的那样失败。

我还创建了一个小型测试项目来演示我的问题。该项目可以在这里找到 – Github .

提前致谢。

Answer 1

在过去的几年里，我断断续续地生活在类似的情况下。

为了解决这个问题，我使用以下 build.gradle 文件创建了一个示例迷你项目:

apply plugin: 'groovy'

repositories { 
  jcenter()
  mavenCentral()
}

dependencies { 
    compile "org.codehaus.groovy:groovy:2.4.15"
}



if (JavaVersion.current() != JavaVersion.VERSION_1_6) {
  // findJava6Jvm is defined in java-versions.gradle
  // and returns a gradle JavaInfo instance.
  def java6Jvm = findJava6Jvm()

  if (!rootProject.ext.has('hasPrintedJavaVersionNote')) {
    println "**************** java version notice ****************"
    println "NOTE: the gradle process and the source compilation"
    println "      are using different versions of java:"
    println ""
    println "    gradle process uses:       ${JavaVersion.current()}"
    println "    source complilation uses:  1.6"
    println ""
    println "*****************************************************"
    rootProject.ext.hasPrintedJavaVersionNote = true
  }

  sourceCompatibility = JavaVersion.VERSION_1_6
  targetCompatibility = JavaVersion.VERSION_1_6

  tasks.withType(AbstractCompile) {
    options.with {
      fork = true
      forkOptions.executable = java6Jvm.javacExecutable
    }
  }

  tasks.withType(GroovyCompile) {
    groovyOptions.with {
      fork = true
    }
  }

  tasks.withType(Javadoc) {
    executable = java6Jvm.javadocExecutable
  }

  tasks.withType(Test) {
    executable = java6Jvm.javaExecutable
  }

  tasks.withType(JavaExec) {
    executable = java6Jvm.javaExecutable
  }
}


def findJava6Jvm(Closure extraUsage = null) {
  if (JavaVersion.current().isJava6()) {
    // if we are already using java 6 to launch gradle, just return 
    // the javac for the current jvm
    return org.gradle.internal.jvm.Jvm.current()
  }

  def failOnCondition = { condition, msg -> 
    if (condition) {
      println """
      Executing the gradle build with a JDK different from java 1.6
      (i.e. java 7, 8, etc) requires that you provide the build 
      with enough information so that it can still locate a java 1.6
      jdk for source code compilation. 

      If the build can not locate a java 6 jdk, you can help it out by 
      specifying one of the following properties: 

        JAVA_HOME_6 environment variable (example: \"export JAVA_HOME_6=/usr/lib/jvm/java-6/\")
        JAVA_HOME_6 system property (-DJAVA_HOME_6=<path>)
        JAVA_HOME_6 gradle project property (-PJAVA_HOME_6=<path>)
      """.stripIndent()  

      if (extraUsage != null) {
        extraUsage()
      }
      println msg.stripIndent()        
      throw new GradleException("No 1.6.x jdk found!") 
    }
  }

  def name = 'JAVA_HOME_6'
  def custom = [System.env[name], System.properties[name], properties[name]].find { it }
  failOnCondition !custom, """
      ERROR: Please set the JAVA_HOME_6 property in one of the above specified
             ways"""

  def jdkDir = file(custom)
  failOnCondition !jdkDir.isDirectory(), """
      ERROR: The configured JAVA_HOME_6 setting:
      
        $custom
      
      does not point to a directory on the local file system.
      Please set this variable to the JAVA_HOME of a 1.6.x
      jdk"""


  def fs = File.separator
  def jdkJavac = file("$jdkDir${fs}bin${fs}javac").canonicalFile
  if( !jdkJavac.isFile() ) jdkJavac = file( jdkJavac.path + ".exe" )

  failOnCondition !jdkJavac.isFile(), """
      ERROR: Could not locate a bin/javac executable file under 
             the configured JAVA_HOME_6 setting: 
    
        $custom \n"""

  def process = [jdkJavac, "-version"].execute()
  process.waitForOrKill(5000)
  def version = process.err.text.readLines().first()
  failOnCondition !version?.contains('1.6.'), """
      ERROR: The configured JAVA_HOME_6 setting:
    
        $custom
    
      points at a non 1.6 jdk, 'java -version' reports $version!"""

  // after all the validations pass, reutrn the jdk javac path
  org.gradle.internal.jvm.Jvm.forHome(jdkDir)
}

我把你问题中的类(class)放到了一个文件中:

java-version-experiment ~> tree src/
src/
└── main
    └── groovy
        └── com
            └── somepackage
                └── SomeGroovyClass.groovy

鉴于上述情况，当我使用 java 8 运行我的源代码的 gradle 编译时:

java-version-experiment ~>  export JAVA_HOME_6=/usr/lib/jvm/java-6_121-oracle

java-version-experiment ~>  setjava java-8-oracle 
PATH updated - JAVA_HOME=/usr/lib/jvm/java-8-oracle

java-version-experiment ~> gradle -v

------------------------------------------------------------
Gradle 4.10.2
------------------------------------------------------------

Build time:   2018-09-19 18:10:15 UTC
Revision:     b4d8d5d170bb4ba516e88d7fe5647e2323d791dd

Kotlin DSL:   1.0-rc-6
Kotlin:       1.2.61
Groovy:       2.4.15
Ant:          Apache Ant(TM) version 1.9.11 compiled on March 23 2018
JVM:          1.8.0_201 (Oracle Corporation 25.201-b09)
OS:           Linux 4.18.0-17-generic amd64


java-version-experiment ~>  gradle build

> Configure project :
**************** java version notice ****************
NOTE: the gradle process and the source compilation
      are using different versions of java:

    gradle process uses:       1.8
    source complilation uses:  1.6

*****************************************************

BUILD SUCCESSFUL in 1s
2 actionable tasks: 2 executed

java-version-experiment ~>  

似乎该类确实是使用 java 6 编译的。在 linux 上，您可以在类文件上使用命令行十六进制编辑器进行检查:

~> od -j 7 -N 1 -t d1 build/classes/groovy/main/com/somepackage/SomeGroovyClass.class 
0000007   50
0000010
~> 

本质上是从类文件中提取字节 7(从零开始)，其中 50 是我们感兴趣的内容。相关的 java 版本号是:

Java 6 uses major version 50
Java 7 uses major version 51
Java 8 uses major version 52
Java 9 uses major version 53
Java 10 uses major version 54
Java 11 uses major version 55

换句话说，在我看来，在编译任务上使用 forkOptions.executable 是可行的，并且这些类确实是使用 java 6 编译的。

但是，在我看来，类路径也会泄漏。我的意思是，似乎即使您使用 java 6 可执行文件进行编译，java 8 类路径和 API 也会泄漏到编译过程中。

如您所说，上面的编译应该失败了，但没有。我仍然不知道为什么会发生这种情况，更重要的是如何防止类路径泄漏。

任何 gradle 专家请随时在这里发表意见，我很想弄清这个问题的真相。

<<编辑>>

找到以下内容:

Compiling and testing for Java 6 or Java 7

The Groovy compiler will always be executed with the same version of Java that was used to start Gradle. You should set sourceCompatibility and targetCompatibility to 1.6 or 1.7. If you also have Java source files, you can follow the same steps as for the Java plugin to ensure the correct Java compiler is used.

在 gradle 文档中:

https://docs.gradle.org/current/userguide/groovy_plugin.html

所以这对于 groovy 来说似乎是不可能的。类文件中的第 7 个字节似乎由以下内容控制:

targetCompatibility = JavaVersion.VERSION_1_6

设置，即即使使用纯 Java 8 并设置 targetCompatibility，我们也会在类主要版本字节中得到 50。

<<编辑2>>

验证这适用于 java 文件。在 src/main/java/com/somepackage/SomeJavaClass.java 下添加了一个 java 文件，其构建文件与上面配置的双 vm 编译场景完全相同。

结果:

gradle clean build

> Configure project :
**************** java version notice ****************
NOTE: the gradle process and the source compilation
      are using different versions of java:

    gradle process uses:       1.8
    source complilation uses:  1.6

*****************************************************

> Task :compileJava FAILED
/home/mbjarland/projects/java-version-experiment/src/main/java/com/somepackage/SomeJavaClass.java:5: cannot find symbol
symbol  : class Optional
location: class com.somepackage.SomeJavaClass
    public Optional<String> someJavaMethod() {
           ^
/home/mbjarland/projects/java-version-experiment/src/main/java/com/somepackage/SomeJavaClass.java:6: cannot find symbol
symbol  : variable Optional
location: class com.somepackage.SomeJavaClass
        return Optional.empty();
               ^
2 errors

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileJava'.
> Compilation failed with exit code 1; see the compiler error output for details.

BUILD FAILED in 1s
2 actionable tasks: 2 executed

这是你所期望的。

经过长时间探索后的结论:这对 java 文件有效，但对 groovy 文件无效。