java - Gradle compileJava task warning: [options] bootstrap class path not set in conjunction with -source 1.6

Question

Below is the content of the build.gradle file:

apply plugin: 'java'

archivesBaseName    = 'foo-bar'
version             = '1.0'
sourceCompatibility = JavaVersion.VERSION_1_6
targetCompatibility = JavaVersion.VERSION_1_6

sourceSets.main.resources.exclude 'foo.jks'

compileJava{
    println project.sourceCompatibility 
    println project.targetCompatibility 
    println sourceCompatibility 
    println targetCompatibility 
}

And below is the result of running the Gradle jar task:

[sts] -----------------------------------------------------
[sts] Starting Gradle build for the following tasks: 
[sts]      :jar
[sts] -----------------------------------------------------
1.6
1.6
1.6
1.6
:compileJavawarning: [options] bootstrap class path not set in conjunction with -source 1.6
1 warning

:processResources UP-TO-DATE
:classes
:jar

BUILD SUCCESSFUL

Total time: 1 mins 3.072 secs
[sts] -----------------------------------------------------
[sts] Build finished succesfully!
[sts] Time taken: 1 min, 3 sec
[sts] -----------------------------------------------------

Although it claims that the build was successful, the warning has me a little worried about run-time complications. How do I resolve this warning?

Also, I'm using Eclipse Indigo. And I have the Java compiler and build path of my project set to jdk1.6.0_35.

If anyone needs more information, please let me know!

---

UPDATE

I navigated to Window > Preferences > Gradle and I set "Java Home" to the "Workspace JRE" jdk1.6.0_35,

And now I get the following output when I run the Gradle jar task,

[sts] -----------------------------------------------------
[sts] Starting Gradle build for the following tasks: 
[sts]      :jar
[sts] -----------------------------------------------------
1.6
1.6
1.6
1.6
:compileJavawarning: javalangEnum.class(javalang:Enum.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangComparable.class(javalang:Comparable.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangObject.class(javalang:Object.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaioSerializable.class(javaio:Serializable.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangString.class(javalang:String.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaioInputStream.class(javaio:InputStream.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecurityKeyStore.class(javasecurity:KeyStore.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaxcryptoCipher.class(javaxcrypto:Cipher.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaxcryptospecSecretKeySpec.class(javaxcryptospec:SecretKeySpec.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaxxmlindDatatypeConverter.class(javaxxmlind:DatatypeConverter.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangCloneNotSupportedException.class(javalang:CloneNotSupportedException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangClass.class(javalang:Class.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangClassLoader.class(javalang:ClassLoader.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecurityKeyStore$LoadStoreParameter.class(javasecurity:KeyStore$LoadStoreParameter.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaioCloseable.class(javaio:Closeable.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangAutoCloseable.class(javalang:AutoCloseable.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangException.class(javalang:Exception.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangThrowable.class(javalang:Throwable.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecuritycertCertificate.class(javasecuritycert:Certificate.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecurityKey.class(javasecurity:Key.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecurityspecKeySpec.class(javasecurityspec:KeySpec.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaxcryptoSecretKey.class(javaxcrypto:SecretKey.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangError.class(javalang:Error.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecurityKeyStoreException.class(javasecurity:KeyStoreException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecurityGeneralSecurityException.class(javasecurity:GeneralSecurityException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangRuntimeException.class(javalang:RuntimeException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaioIOException.class(javaio:IOException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecurityNoSuchAlgorithmException.class(javasecurity:NoSuchAlgorithmException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecuritycertCertificateException.class(javasecuritycert:CertificateException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaxcryptoNoSuchPaddingException.class(javaxcrypto:NoSuchPaddingException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecurityInvalidKeyException.class(javasecurity:InvalidKeyException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javasecurityKeyException.class(javasecurity:KeyException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: java
ioByteBuffer.class(java
io:ByteBuffer.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaxcryptoIllegalBlockSizeException.class(javaxcrypto:IllegalBlockSizeException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javaxcryptoBadPaddingException.class(javaxcrypto:BadPaddingException.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangStringBuilder.class(javalang:StringBuilder.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangAbstractStringBuilder.class(javalang:AbstractStringBuilder.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangCharSequence.class(javalang:CharSequence.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
warning: javalangStringBuffer.class(javalang:StringBuffer.class): major version 51 is newer than 50, the highest major version supported by this compiler.
It is recommended that the compiler be upgraded.
39 warnings

:processResources UP-TO-DATE
:classes
:jar

BUILD SUCCESSFUL

Total time: 1.96 secs
[sts] -----------------------------------------------------
[sts] Build finished succesfully!
[sts] Time taken: 0 min, 1 sec
[sts] -----------------------------------------------------

What do?

Answer 1

You can bootstrap class path using bootClasspath option:

apply plugin: 'java'

sourceCompatibility = 1.6
targetCompatibility = 1.6

compileJava.options.bootClasspath = "$JDK6_HOME/jre/lib/rt.jar"

To set the bootClasspath option on all compile tasks in the project you can use the withType() method on the TaskContainer to find all tasks of type Compile:

apply plugin: 'java'

sourceCompatibility = 1.6
targetCompatibility = 1.6

tasks.withType(JavaCompile) {
    options.bootstrapClasspath = files("$JDK6_HOME/jre/lib/rt.jar")
}

gradle.properties:

JDK6_HOME=C:/JAVA/jdk6

See documentation for details.