关于JNI程序中引用另外一个lib

我最近在写一个j2se的程序，我用的是开源的org.amse.ys.zip包里的代码，这部分代码是在FBReaderJ里抽取的，但是其中包含了一些native的方法，需要用的zlib库，而FBReaderJ由于是运行在Android平台上的，它对应的so库肯定是无法在我的程序中使用，因此，在这里下载了zlib的win32运行库后，我使用

 javah -jni org.amse.ys.zip.DeflatingDecompressor

生成了org_amse_ys_zip_DeflatingDecompressor.h 头文件，内容如下：

 /* DO NOT EDIT THIS FILE - it is machine generated */
 #include "jni.h"
 /* Header for class org_amse_ys_zip_DeflatingDecompressor */

 #ifndef _Included_org_amse_ys_zip_DeflatingDecompressor
 #define _Included_org_amse_ys_zip_DeflatingDecompressor
 #ifdef __cplusplus
 extern "C" {
 #endif
 #undef org_amse_ys_zip_DeflatingDecompressor_IN_BUFFER_SIZE
 #define org_amse_ys_zip_DeflatingDecompressor_IN_BUFFER_SIZE 2048L
 #undef org_amse_ys_zip_DeflatingDecompressor_OUT_BUFFER_SIZE
 #define org_amse_ys_zip_DeflatingDecompressor_OUT_BUFFER_SIZE 32768L
 /*
  * Class:     org_amse_ys_zip_DeflatingDecompressor
  * Method:    startInflating
  * Signature: ()I
  */
 JNIEXPORT jint JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_startInflating
   (JNIEnv *, jobject);

 /*
  * Class:     org_amse_ys_zip_DeflatingDecompressor
  * Method:    endInflating
  * Signature: (I)V
  */
 JNIEXPORT void JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_endInflating
   (JNIEnv *, jobject, jint);

 /*
  * Class:     org_amse_ys_zip_DeflatingDecompressor
  * Method:    inflate
  * Signature: (I[BII[B)J
  */
 JNIEXPORT jlong JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_inflate
   (JNIEnv *, jobject, jint, jbyteArray, jint, jint, jbyteArray);

 #ifdef __cplusplus
 }
 #endif
 #endif

建立VS2005 DLL工程，加入jni.h, jni_md.h, zlib的 zconf.h, 加入zdll.lib依赖，加入DeflatingDecompressor.cpp:

 /*
  * Copyright (C) 2009-2013 Geometer Plus <contact@geometerplus.com>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  * 02110-1301, USA.
  */
 #include <string.h>
 #include "zlib.h"

 #include <new>
 #include "jni.h"
 #include "org_amse_ys_zip_DeflatingDecompressor.h"

 #define                                SIZE                            10

 static z_stream*            ourStreams[SIZE]            = {  };

 extern "C"
 JNIEXPORT jint JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_startInflating(JNIEnv *env, jobject thiz) {
     int i;
     for (i = ; i < SIZE; ++i) {
         if (ourStreams[i] == ) {
             ourStreams[i] = new z_stream;
             memset(ourStreams[i], , sizeof(z_stream));
             inflateInit2(ourStreams[i], -MAX_WBITS);
             return i;
         }
     }
     return -;
 }

 extern "C"
 JNIEXPORT void JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_endInflating(JNIEnv *env, jobject thiz, jint inflatorId) {
     if (inflatorId >=  && inflatorId < SIZE) {
         inflateEnd(ourStreams[inflatorId]);
         delete ourStreams[inflatorId];
         ourStreams[inflatorId] = ;
     }
 }

 // returns (endFlag << 32) + ((used inLength) << 16) + outLength
 extern "C"
 JNIEXPORT jlong JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_inflate(JNIEnv *env, jobject thiz, jint inflatorId, jbyteArray in, jint inOffset, jint inLength, jbyteArray out) {
     if (inflatorId <  || inflatorId >= SIZE) {
         return -;
     }
     z_stream *stream = ourStreams[inflatorId];
     if (stream == ) {
         return -;
     }

     jbyte* inStart = env->GetByteArrayElements(in, );
     jbyte* outStart = env->GetByteArrayElements(out, );
     stream->next_in = (Bytef*)inStart + inOffset;
     stream->avail_in = inLength;
     stream->next_out = (Bytef*)outStart;
     const int outLength = env->GetArrayLength(out);
     stream->avail_out = outLength;
     const int code = inflate(stream, Z_SYNC_FLUSH);
     env->ReleaseByteArrayElements(in, inStart, );
     env->ReleaseByteArrayElements(out, outStart, );
     if (code == Z_OK || code == Z_STREAM_END) {
         jlong result = ((inLength - stream->avail_in) << ) + outLength - stream->avail_out;
         if (code == Z_STREAM_END) {
             result |= ((jlong)) << ;
         }
         return result;
     }
     return - + code;
 }

成功编译出DeflatingDecompressor.dll文件。

然后在的j2se工程的DeflatingDecompressor.java中使用

 static {
     System.loadLibrary("libs/DeflatingDecompressor");
 }

加载动态库，得到

 Exception in thread "main" java.lang.UnsatisfiedLinkError: D:\Works\TextLayout\NewReaderSE\libs\DeflatingDecompressor.dll: Can't find dependent libraries
     at java.lang.ClassLoader$NativeLibrary.load(Native Method)
     at java.lang.ClassLoader.loadLibrary0(Unknown Source)
     at java.lang.ClassLoader.loadLibrary(Unknown Source)
     at java.lang.Runtime.loadLibrary0(Unknown Source)
     at java.lang.System.loadLibrary(Unknown Source)
     at org.amse.ys.zip.DeflatingDecompressor.<clinit>(DeflatingDecompressor.java:)

使用 DependencyWalker 查看DeflatingDecompressor.dll的依赖关系，发现缺少zlib1.dll, 这时候我想起来下载的zlib发布中还有一个动态库，拷贝到System32文件夹下，再试，果然可以了。

那么这时候为什么呢？经过资料查询才知道VS编译出来的lib文件有静态和动态lib的区别，简单的说：静态lib就是把所有的代码一股脑编译进lib文件中，在使用的时候配合头文件和lib文件就可以直接用了。而动态lib则是伴随着dll生成的，其中只包含了动态加载dll的代码，通过在程序中引用它，就可以省去了显式的调用dll的繁琐。

如何判断一个lib是静态还是动态的呢？我没有找到好的办法，一般来说，静态lib的发布只有两个文件：一个头文件定义了lib中的开放接口，一个.lib文件则是实现的内容；而动态lib的文件发布包含一个头文件，一个dll文件，一个lib文件，往往还有一个def文件来列出dll中的接口。根据这个就可以判断了。

好了，这就是调用没有成功的原因，我本来已经加载的lib是一个静态lib, 其实它是一个动态lib