Jni FindClass返回NULL

Question

我在头文件中得到了c ++结构,

struct StatusLine
{
    static jclass Class; // Lorg/apache/http/StatusLine;
    static jmethodID GetStatusCode; // ()I
};

struct ByteArrayOutputStream 
{
    static jclass Class; // Ljava/io/ByteArrayOutputStream;
    static jmethodID Constructor; // ()V
    static jmethodID Close; // ()V
    static jmethodID ToByteArray; // ()[B
};

struct HttpEntity
{
    static jclass Class; // Lorg/apache/http/HttpEntity;
    static jmethodID WriteTo; // (Ljava/io/OutputStream;)V
    static jmethodID GetContent; // ()Ljava/io/InputStream;
};  

和cpp文件是

 #define JAVA_STATUS_LINE_CLASS             "org/apache/http/StatusLine"
 #define JAVA_HTTP_ENTITY_CLASS             "org/apache/http/HttpEntity"
 #define JAVA_BYTE_ARRAY_OUTPUT_STREAM_CLASS "java/io/ByteArrayOutputStream"

 jclass StatusLine::Class = 0;
 jmethodID StatusLine::GetStatusCode = 0;

 jclass  ByteArrayOutputStream::Class = 0;
 jmethodID ByteArrayOutputStream::Constructor = 0;
 jmethodID ByteArrayOutputStream::Close = 0;
 jmethodID ByteArrayOutputStream::ToByteArray = 0;

 jclass HttpEntity::Class = 0;
 jmethodID HttpEntity::WriteTo = 0;
 jmethodID HttpEntity::GetContent = 0;

 void initializeJniPointers()
 {
      StatusLine::Class = GetJniEnv()->FindClass(JAVA_STATUS_LINE_CLASS);
      StatusLine::GetStatusCode = GetJniEnv()->GetMethodID(StatusLine::Class, "getStatusCode", "()I");


      ByteArrayOutputStream::Class = GetJniEnv()->FindClass(JAVA_BYTE_ARRAY_OUTPUT_STREAM_CLASS);
      ByteArrayOutputStream::Constructor = GetJniEnv()->GetMethodID(ByteArrayOutputStream::Class, "<init>", "()V");
      ByteArrayOutputStream::Close = GetJniEnv()->GetMethodID(ByteArrayOutputStream::Class, "close", "()V");
      ByteArrayOutputStream::ToByteArray = GetJniEnv()->GetMethodID(ByteArrayOutputStream::Class, "toByteArray", "()[B");

      HttpEntity::Class = GetJniEnv()->FindClass(JAVA_HTTP_ENTITY_CLASS);
      HttpEntity::WriteTo = GetJniEnv()->GetMethodID(HttpEntity::Class, "writeTo", "(Ljava/io/OutputStream;)V");
      HttpEntity::GetContent = GetJniEnv()->GetMethodID(HttpEntity::Class, "getContent", "()Ljava/io/InputStream;");
 }

function initializeJniPointers()粉碎在线StatusLine :: GetStatusCode = GetJniEnv() - > GetMethodID(); 因为StatusLine :: Class为NULL.但!我注意到:如果我在项目StatusLine的一些java文件中写这个l = new StatuLine(){...}

功能上ByteArrayOutputStream击碎::构造,因为ByteArrayOutputStream ::类为null,如果我用Java创建ByteArrayOutputStream的对象,功能将进一步进入下一个对象,等等...我注意到:如果我只声明ByteArrayOutputStream的变量,findClass将返回NULL.

有人可以解释一下该怎么办？BTW我使用Android 2.3.5设备三星GT-S5363,我尝试了其他Android(老人)和设备的转换,它工作正常.

Answer 1

基本上,如果您要求FindClass的线程不是主线程并且在您的线程系统中没有构建java类ID的映射,则会发生这种情况.

检查一下,可能你必须先在主线程中询问FindClass(当JNI加载或其他地方时),然后你就可以在任何线程中执行此操作.

http://discuss.cocos2d-x.org/t/jni-findclass-cannot-find-a-class-if-its-called-by-a-new-pthread/1873/4

也试试这个,这对我有用:https: //svn.apache.org/repos/asf/mesos/branches/0.10.x/src/java/jni/convert.cpp

解决方案(取自上面的链接)是从JNI_OnLoad中的应用程序中找到Java类加载器,然后让他从任何线程中找到类.否则,在调用env-> FindClass之后,JNI可以回退到只加载像String这样的系统类的系统类加载器.