[Bug][JAVA]: maven failed to build libgar-jni.so

[acezen]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

build the java sdk with maven got error:

[exec] /usr/lib/llvm-11/bin/clang++  -Dgar_jni_EXPORTS -I/home/john/GraphAr/java/src/main/native -I/home/j
ohn/GraphAr/java/src/test/native -isystem /home/john/GraphAr/java/target/native/graphar_ep-prefix/include -isystem /us
r/lib/jvm/java-8-openjdk-amd64/include -isystem /usr/lib/jvm/java-8-openjdk-amd64/include/linux  -flto -fforce-emit-vt
ables -O3 -g -std=c++17 -Wall -fPIC   -pthread -std=gnu++17 -o CMakeFiles/gar-jni.dir/target/generated-sources/annotat
ions/jni_com_alibaba_graphar_writers_builder_VerticesBuilder_cxx_0xd05edbb.cc.o -c /home/john/GraphAr/java/target/gene
rated-sources/annotations/jni_com_alibaba_graphar_writers_builder_VerticesBuilder_cxx_0xd05edbb.cc
[INFO]      [exec] make[2]: Leaving directory '/home/john/GraphAr/java/target/native'
[INFO]      [exec] make[1]: Leaving directory '/home/john/GraphAr/java/target/native'
[INFO]      [exec] make[2]: *** No rule to make target 'graphar_ep-prefix/lib/libgar.so', needed by 'libgar-jni.so'.  
Stop.
[ERROR] /home/john/GraphAr/java/build.xml:24: exec returned: 2
[ERROR] around Ant part ...<ant antfile="/home/john/GraphAr/java/build.xml">... @ 5:54 in /home/john/GraphAr/java/targ
et/antrun/build-main.xml

Expected Behavior

build successful without error.

Minimal Reproducible Example

maven clean test

Environment

• Operating system: Ubuntu 20.04
• CMake version: 3.16.3
• GraphAr version: commit

Link to GraphAr Logs

No response

Further Information

No response

[acezen]

This issue is reported by @Thespica

[acezen]

After digging into @Thespica 's building environment, seems that the generated MakeFile of java's CMakeList has the wrong building order:
Makefile2.txt

# The main recursive "all" target.
all: CMakeFiles/gar-jni.dir/all
all: CMakeFiles/graphar_ep.dir/all

.PHONY : all

# The main recursive "preinstall" target.
preinstall:

.PHONY : preinstall

# The main recursive "clean" target.
clean: CMakeFiles/gar-jni.dir/clean
clean: CMakeFiles/graphar_ep.dir/clean

gar-jni target depends on target graphar， but the building order is wrong.

After debugging, the code:
https://github.com/alibaba/GraphAr/blob/c3ced985b49a9c2be6aaff7acc287dc9a870cdec/java/CMakeLists.txt#L28
it links the graphar with a variable name, this could be empty if graphar not building yet.
Here should use the imported target name to enforce the graphar building before gar-jni.