我已经在c ++代码中成功实现了JNI。当我导入名为xeger.jar的外部jar文件并在java代码中使用其函数时，会出现此问题。即使我使用外部库，使用ecllipse运行它时，java文件上的代码也会运行。但是当我在c ++代码中使用JNI调用它时，它不会按预期返回值。
我有以下java类
package cversion.xeger.implementation;
import nl.flotsam.xeger.Xeger;
public class StringGenerator {
public static int giveMeNumber(int x) {
int y = 33;
String regex = "[1-9]\\|[1-9][0-9]{1,5}\\|1000000";
Xeger generator = new Xeger(regex);
String result = generator.generate();
System.out.println("Hurrayyyyyyyy !!!!!!!!!!!!!!" + result);
return y;
}
}
我的c ++代码如下：
#include <iostream>
#include "jni.h"
#include <string.h>
#include <typeinfo>
int main()
{
JavaVMOption options[1];
JNIEnv *env;
JavaVM *jvm;
JavaVMInitArgs vm_args;
long status;
jclass cls;
jmethodID mid;
jint square;
jboolean answer;
// options[0].optionString = const_cast<char *>("-Djava.library.path=/usr/lib/jvm/java-8-oracle/lib/amd64:/usr/lib/jvm/java-8-oracle/jre/lib/amd64/server");
options[0].optionString = const_cast<char *>("-Djava.class.path=/home/aaa/eclipse-workspace/xeger/target/classes:/home/aaa/Downloads/automaton-1.12/dist/automation.jar:/home/aaa/Downloads/dxeger-1.0-SNAPSHOT.jar");
// options[0].optionString = const_cast<char *>("-Djava.class.path=/home/aaa/Desktop/classpath-try/");
// options[0].optionString = const_cast<char *>("-Djava -cp /home/aaa/Desktop/Untitled.jar");
memset(&vm_args, 0, sizeof(vm_args));
vm_args.version = JNI_VERSION_1_8;
vm_args.nOptions = 1;
vm_args.options = options;
status = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args); //If JVM creation is successful then status value is zero
std::cout<<"Status of JNI creation is : "<<status<<std::endl;
if (status != JNI_OK)
{
std::cout<<"JNI creation Failed : "<<std::endl;
return 1;
}
std::cout<<"JNI creation Passed : "<<std::endl;
cls = env->FindClass("cversion/xeger/implementation/StringGenerator"); // If the class cannot be found, cls will be zero.
std::cout<<"The class of cls is : "<<typeid(cls).name()<<std::endl;
// cls = env->FindClass("Sample2");
std::cout<<"The value of cls is : "<<cls<<std::endl;
if(cls !=0)
{
mid = env->GetStaticMethodID(cls, "giveMeNumber", "(I)I");
std::cout<<"The value of mid is : "<<mid<<std::endl;
if(mid !=0)
{ square = env->CallStaticIntMethod(cls, mid, 25);
std::cout<<"The value of square is "<<square<<std::endl;
printf("Result of implementation : %d\n", square);
}
}
jvm->DestroyJavaVM();
return 0;
}
当我运行c ++文件时，行：
printf("Result of intMethod: %d\n", square);
打印0.应该打印33。
现在，如果我从java文件中删除以下代码，则会打印33。
String regex = "[1-9]\\|[1-9][0-9]{1,5}\\|1000000";
Xeger generator = new Xeger(regex);
String result = generator.generate();
System.out.println("Hurrayyyyyyyy !!!!!!!!!!!!!!" + result);
答案 0 :(得分：1)
对我来说效果很好：
lib/main
Status of JNI creation is : 0
JNI creation Passed :
The class of cls is : P7_jclass
The value of cls is : 0x7f9b26c0d0b0
The value of mid is : 0x7f9b26c28230
Hurrayyyyyyyy !!!!!!!!!!!!!!3|27654|1000000
The value of square is 33
Result of implementation : 33
在您的代码中执行以下操作：
int y = 33;
try {
String regex = "[1-9]\\|[1-9][0-9]{1,5}\\|1000000";
Xeger generator = new Xeger(regex);
String result = generator.generate();
System.out.println("Hurrayyyyyyyy !!!!!!!!!!!!!!" + result);
} catch(Throwable ex) {
ex.printStackTrace();
}
return y;
并且错误将显示出来;）
我打赌你会得到：
java.lang.NoClassDefFoundError: dk/brics/automaton/RegExp
at nl.flotsam.xeger.Xeger.<init>(Xeger.java:45)
看看这里，完全可重复的用例：
.
├── Makefile
├── Makefile.common
├── c
│ └── main.cc
├── jar
│ ├── automaton.jar
│ └── xeger-1.0-SNAPSHOT.jar
├── java
│ └── simple
│ └── JavaCode.java
├── lib
└── target
你需要main.cc
#include <iostream>
#include "jni.h"
#include <string.h>
#include <typeinfo>
int main()
{
JavaVMOption options[1];
JNIEnv *env;
JavaVM *jvm;
JavaVMInitArgs vm_args;
options[0].optionString = const_cast<char *>("-Djava.class.path=./target:./jar/xeger-1.0-SNAPSHOT.jar:./jar/automaton.jar");
memset(&vm_args, 0, sizeof(vm_args));
vm_args.version = JNI_VERSION_1_8;
vm_args.nOptions = 1;
vm_args.options = options;
long status = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);
std::cout << "Status of JNI creation is : "
<< status
<< std::endl;
if( status != JNI_OK ) {
std::cout << "JNI creation Failed : "
<< std::endl;
return 1;
}
std::cout << "JNI creation Passed : "
<< std::endl;
jclass cls = env->FindClass("simple/JavaCode");
std::cout << "The class of cls is : "
<< typeid(cls).name()
<< std::endl
<< "The value of cls is : "
<< cls
<< std::endl;
if( cls != 0 ) {
jmethodID mid = env->GetStaticMethodID(cls, "giveMeNumber", "(I)I");
std::cout << "The value of mid is : "
<< mid
<< std::endl;
if( mid != 0 ) {
jint square = env->CallStaticIntMethod(cls, mid, 25);
std::cout << "The value of square is "
<< square
<< std::endl;
printf("Result of implementation : %d\n", square);
} else {
return 1;
}
} else {
return 1;
}
jvm->DestroyJavaVM();
return 0;
}
和Java代码
package simple;
import nl.flotsam.xeger.Xeger;
public class JavaCode {
public static int giveMeNumber(int x) {
int y = 33;
try {
String regex = "[1-9]\\|[1-9][0-9]{1,5}\\|1000000";
Xeger generator = new Xeger(regex);
String result = generator.generate();
System.out.println("Hurrayyyyyyyy !!!!!!!!!!!!!!" + result);
} catch(Throwable ex) {
ex.printStackTrace();
}
return y;
}
}
<强> 1。基于LLVM的设置
我使用make来构建代码，因为我同时编译了Java和本机代码。所以，你需要Makefile.common
ARCH=$(shell uname -s | tr '[:upper:]' '[:lower:]')
ifeq ($(ARCH),darwin)
EXT=dylib
else
EXT=so
endif
和Makefile。选项卡要小心！ Make require tab是每一行目标的第一个字符。
include ./Makefile.common
ifeq ($(ARCH),darwin)
CC=llvm-g++
MAC_OS_FLAGS=-rpath ${JAVA_HOME}/jre/lib/server -L/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -dynamic -arch x86_64 -lSystem
else
CC=g++
MAC_OS_FLAGS=
endif
all: lib/main target/simple/JavaCode.class
target/simple/JavaCode.class: java/simple/JavaCode.java
$(JAVA_HOME)/bin/javac -cp ./jar/xeger-1.0-SNAPSHOT.jar -d target $<
lib/main.o: c/main.cc
$(CC) -c -o $@ $^ -I${JAVA_HOME}/include -I${JAVA_HOME}/include/$(ARCH)
lib/main: lib/main.o
llvm-g++ -v -o $@ -L${JAVA_HOME}/jre/lib/server/ -ljvm $(MAC_OS_FLAGS) $^
test: lib/main target/simple/JavaCode.class
lib/main
clean:
-rm -rfv target/*
-rm -rf lib/*
然后，您可以致电make test
llvm-g++ -c -o lib/main.o c/main.cc ...
...
...
lib/main
Status of JNI creation is : 0
JNI creation Passed :
The class of cls is : P7_jclass
The value of cls is : 0x7f895ec0d440
The value of mid is : 0x7f895ee11af0
Hurrayyyyyyyy !!!!!!!!!!!!!!5|64|1000000
The value of square is 33
Result of implementation : 33
您可以在此处找到许多不同的JNI代码：JNI Cookbook
<强> 2。基于GNU的设置
如果是基于GNU的设置（例如在Linux中），您可以截断Makefile并删除Makefile.common。
CC=g++
all: lib/main target/simple/JavaCode.class
target/simple/JavaCode.class: java/simple/JavaCode.java
$(JAVA_HOME)/bin/javac -cp ./jar/xeger-1.0-SNAPSHOT.jar -d target $<
lib/main.o: c/main.cc
$(CC) -c -o $@ $^ -I${JAVA_HOME}/include -I${JAVA_HOME}/include/linux
lib/main: lib/main.o
$(CC) -v -o $@ -L${JAVA_HOME}/jre/lib/amd64/server/ -ljvm $^
test: lib/main target/simple/JavaCode.class
lib/main
clean:
-rm -rfv target/*
-rm -rf lib/*
当然，您还必须确保下载jar（进入jar目录）
curl -O \
"http://www.brics.dk/automaton/automaton.jar"
curl -O \
"https://storage.googleapis.com/google-code-archive-downloads/v2/code.google.com/xeger/xeger-1.0-SNAPSHOT.jar"
然后只需致电make test
make test
lib/main
Status of JNI creation is : 0
JNI creation Passed :
The class of cls is : P7_jclass
The value of cls is : 0x136b810
The value of mid is : 0x148fdc0
Hurrayyyyyyyy !!!!!!!!!!!!!!6|756293|1000000
The value of square is 33
Result of implementation : 33