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]            = { 0 };

extern "C"
JNIEXPORT jint JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_startInflating(JNIEnv *env, jobject thiz) {
int i;
for (i = 0; i < SIZE; ++i) {
if (ourStreams[i] == 0) {
ourStreams[i] = new z_stream;
memset(ourStreams[i], 0, sizeof(z_stream));
inflateInit2(ourStreams[i], -MAX_WBITS);
return i;
}
}
return -1;
}

extern "C"
JNIEXPORT void JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_endInflating(JNIEnv *env, jobject thiz, jint inflatorId) {
if (inflatorId >= 0 && inflatorId < SIZE) {
inflateEnd(ourStreams[inflatorId]);
delete ourStreams[inflatorId];
ourStreams[inflatorId] = 0;
}
}

// 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 < 0 || inflatorId >= SIZE) {
return -1;
}
z_stream *stream = ourStreams[inflatorId];
if (stream == 0) {
return -2;
}

jbyte* inStart = env->GetByteArrayElements(in, 0);
jbyte* outStart = env->GetByteArrayElements(out, 0);
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, 0);
env->ReleaseByteArrayElements(out, outStart, 0);
if (code == Z_OK || code == Z_STREAM_END) {
jlong result = ((inLength - stream->avail_in) << 16) + outLength - stream->avail_out;
if (code == Z_STREAM_END) {
result |= ((jlong)1) << 32;
}
return result;
}
return -1024 + 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:7)

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