API build fails in WSO2 API Microgateway 3.1.0 - wso2

Question

I am new to WSO2 microgateway and was following the steps given in the documentation : "https://docs.wso2.com/display/MG310/Quick+Start+Guide+-+Binary" for exposing the Petstore service via microgateway.
I was able to initialize the API using the swagger file as given in the steps. The Petstore project is also created under the project directory. But when i try to build the project as given in Step 1.2, it fails with an error as shown below. Need suggestions to resolve this issue.
In the ballerina-internal.log file, i get the below error.
[2020-07-16 21:13:19,009] SEVERE {b7a.log.crash} - Array index out of range: 0
java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 0
at org.ballerinalang.nativeimpl.jvm.interop.JMethodResolver.validateArgumentTypes(JMethodResolver.java:194)
at org.ballerinalang.nativeimpl.jvm.interop.JMethodResolver.validateMethodSignature(JMethodResolver.java:148)
at org.ballerinalang.nativeimpl.jvm.interop.JMethodResolver.resolve(JMethodResolver.java:107)
at org.ballerinalang.nativeimpl.jvm.interop.JInteropMethodValidator.resolveJMethod(JInteropMethodValidator.java:74)
at org.ballerinalang.nativeimpl.jvm.interop.JInteropMethodValidator.validateAndGetJMethod(JInteropMethodValidator.java:61)
at ballerina.jvm.$value$InteropValidator.validateAndGetJMethod(interop.bal:90)
at ballerina.jvm.$value$InteropValidator.call(interop.bal)
at ballerina.compiler_backend_jvm.interop.interop_method_gen.createJMethodWrapper(interop/interop_method_gen.bal:136)
at ballerina.compiler_backend_jvm.interop.interop_method_gen.createJInteropFunctionWrapper(interop/interop_method_gen.bal:128)
at ballerina.compiler_backend_jvm.interop.external_method_gen.createExternalFunctionWrapper(interop/external_method_gen.bal:180)
at ballerina.compiler_backend_jvm.jvm_package_gen.generateClassNameMappings(jvm_package_gen.bal:477)
at ballerina.compiler_backend_jvm.jvm_package_gen.generatePackage(jvm_package_gen.bal:149)
at ballerina.compiler_backend_jvm.jvm_package_gen.generateDependencyList(jvm_package_gen.bal:120)
at ballerina.compiler_backend_jvm.jvm_package_gen.generatePackage(jvm_package_gen.bal:142)
at ballerina.compiler_backend_jvm.jvm_package_gen.generateDependencyList(jvm_package_gen.bal:120)
at ballerina.compiler_backend_jvm.jvm_package_gen.generatePackage(jvm_package_gen.bal:142)
at ballerina.compiler_backend_jvm.jvm_package_gen.generateDependencyList(jvm_package_gen.bal:120)
at ballerina.compiler_backend_jvm.jvm_package_gen.generatePackage(jvm_package_gen.bal:142)
at ballerina.compiler_backend_jvm.jvm_package_gen.generateDependencyList(jvm_package_gen.bal:120)
at ballerina.compiler_backend_jvm.jvm_package_gen.generatePackage(jvm_package_gen.bal:142)
at ballerina.compiler_backend_jvm.main.generateJarBinary(main.bal:86)
at ballerina.compiler_backend_jvm.main.main(main.bal:60)
at ballerina.compiler_backend_jvm.___init.$lambda$main$(compiler_backend_jvm)
at ballerina.compiler_backend_jvm.___init$$Lambda$11.000000001107AEE0.apply(Unknown Source)
at org.ballerinalang.jvm.scheduling.SchedulerItem.execute(Scheduler.java:426)
at org.ballerinalang.jvm.scheduling.Scheduler.run(Scheduler.java:218)
at org.ballerinalang.jvm.scheduling.Scheduler.runSafely(Scheduler.java:191)
at org.ballerinalang.jvm.scheduling.Scheduler$$Lambda$6.0000000010F6DAF0.run(Unknown Source)
at java.lang.Thread.run(Thread.java:813)

Answer 1

Looking at the responses in the comments it looks like the external jdk is not fully compatible with mgw. Not sure on the exact reason though. Here is a bit more background on what going on during the build command and a possible workaround to force mgw use internal jdk.
All mgw distributions (toolkit/runtime) including the binary distribution, contains a jdk internally which is fully compatible with the ballerina version used in the mgw. However during the execution of mgw toolkit command it checks for externally installed jdks (by looking at JAVA_HOME variable) and pick it as the jdk if a compatible version is found in the system. Otherwise it will use the internal jdk.
So to avoid mgw from picking up external jdk, we should set JAVA_HOME variable to "" or invalid location. To do that open micro-gw.bat (assume you are on windows) file in the <TOOLKIT_HOME>/bin directory and around line 55 after SET HOME_CACHE=%MICROGW_HOME%\lib\gateway-balo add SET JAVA_HOME= as command. After the change code block around above line will look like below.
.
.
.
SET PATH=%BALLERINA_HOME%\bin\;%PATH%
SET JAVA_PATH=%MICROGW_HOME%\lib\jdk8u202-b08-jre
SET HOME_CACHE=%MICROGW_HOME%\lib\gateway-balo
REM ******* Below is the line we added to reset the JAVA_HOME *******
SET JAVA_HOME=
REM Check JAVA availability
if EXIST "%JAVA_HOME%" (
ECHO JAVA_HOME: %JAVA_HOME%
.
.
.
Save the file and try the build command again. It should work.