如何通过JNI加载JVM失败时如何收到错误消息？

I would like to retrieve an error message that explains why the jvm failed to load. From the examples provided here:

我想检索一条错误消息,解释为什么jvm无法加载。从这里提供的示例:

http://java.sun.com/docs/books/jni/html/invoke.html

I extracted this example:

我提取了这个例子:

 /* Create the Java VM */
 res = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);

 if (res < 0) {
     // retrieve verbose error here?
     fprintf(stderr, "Can't create Java VM\n");
     exit(1);
 }

In my specific case I'm providing invalid arguments in the vm_args and would expect to see what I get on the command line: "Unrecognized option: -foo=bar"

在我的具体情况下,我在vm_args中提供了无效的参数,并希望看到我在命令行上看到的内容:“无法识别的选项:-foo = bar”

On further testing it looks like the jvm is putting the message I want to stdout or stderr. I believe I would need to capture stdout and stderr to get the error I'm looking for (unless of course there is a simpler way). I'm coding in C++ so if someone can show a way to capture the error into a stringstream that would be ideal.

在进一步测试时,看起来jvm正在将我想要的消息放入stdout或stderr。我相信我需要捕获stdout和stderr来获取我正在寻找的错误(除非当然有一种更简单的方法)。我正在使用C ++进行编码,因此如果有人能够展示将错误捕获到字符串流中的方法,那将是理想的。

Thanks, Randy

3 个解决方案

#1

I was able to get what I needed by using the "vfprintf" option described here:

通过使用此处描述的“vfprintf”选项,我能够获得所需的内容:

http://java.sun.com/products/jdk/faq/jnifaq-old.html

although I used the jdk1.2 options. This code snippet summarizes my solution:

虽然我使用了jdk1.2选项。此代码段总结了我的解决方案:

static string jniErrors;

static jint JNICALL my_vfprintf(FILE *fp, const char *format, va_list args)
{
    char buf[1024];
    vsnprintf(buf, sizeof(buf), format, args);
    jniErrors += buf;
    return 0;
}

...

JavaVMOption options[1];
options[0].optionString = "vfprintf";
options[0].extraInfo = my_vfprintf;

JavaVMInitArgs vm_args;
memset(&vm_args, 0, sizeof(vm_args));
vm_args.nOptions = 1;
vm_args.options = options;
vm_args.version = JNI_VERSION_1_4;
vm_args.ignoreUnrecognized = JNI_FALSE;

JNIEnv env;
JavaVM jvm;

jint res = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);

if (res != JNI_OK)
    setError(jniErrors);

jniErrors.clear();

Also interesting was that I could not for the life of me capture stdout or stderr correctly with any of the freopen or dup2 tricks. I could load my own dll and redirect correctly but not the jvm. Anyway, it's better this way because I wanted the errors in memory rather than in a file.

同样有趣的是,我无法在生活中使用任何freopen或dup2技巧正确捕获stdout或stderr。我可以加载我自己的DLL并正确重定向但不是jvm。无论如何,这种方式更好,因为我想要内存中的错误而不是文件中的错误。

#2

When I wrote this code I would also get the error via stdout/stderr.

当我编写这段代码时,我也会通过stdout / stderr得到错误。

The best way to redirect stdout/stderr in your process is by using freopen. Here is a * question specifically about that subject.

在您的进程中重定向stdout / stderr的最佳方法是使用freopen。这是一个*问题,专门针对该主题。

However, once that call is passed, you will then have a JNIEnv, and all further error checking can and should be done by calling JNIEnv::ExceptionOccurred(), which will may return a Throwable object that you can then interrogate with your JNI code.

但是,一旦调用通过,您将拥有一个JNIEnv,并且所有进一步的错误检查都可以而且应该通过调用JNIEnv :: ExceptionOccurred()完成,这可能会返回一个Throwable对象,然后您可以使用您的JNI代码查询。

#3

After getting a hold of stdout and stderr, which you'll need anyway, add -Xcheck:jni to your jvm command line to get extra jni-related warnings from the jvm.

在获得stdout和stderr之后,无论如何都需要将-Xcheck:jni添加到你的jvm命令行以从jvm获取额外的jni相关警告。

#1