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
1 javah -jni org.amse.ys.zip.DeflatingDecompressor
生成了org_amse_ys_zip_DeflatingDecompressor.h 头文件，内容如下：
1 /* DO NOT EDIT THIS FILE - it is machine generated */ 2 #include "jni.h" 3 /* Header for class org_amse_ys_zip_DeflatingDecompressor */ 4 5 #ifndef _Included_org_amse_ys_zip_DeflatingDecompressor 6 #define _Included_org_amse_ys_zip_DeflatingDecompressor 7 #ifdef __cplusplus 8 extern "C" { 9 #endif 10 #undef org_amse_ys_zip_DeflatingDecompressor_IN_BUFFER_SIZE 11 #define org_amse_ys_zip_DeflatingDecompressor_IN_BUFFER_SIZE 2048L 12 #undef org_amse_ys_zip_DeflatingDecompressor_OUT_BUFFER_SIZE 13 #define org_amse_ys_zip_DeflatingDecompressor_OUT_BUFFER_SIZE 32768L 14 /* 15 * Class: org_amse_ys_zip_DeflatingDecompressor 16 * Method: startInflating 17 * Signature: ()I 18 */ 19 JNIEXPORT jint JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_startInflating 20 (JNIEnv *, jobject); 21 22 /* 23 * Class: org_amse_ys_zip_DeflatingDecompressor 24 * Method: endInflating 25 * Signature: (I)V 26 */ 27 JNIEXPORT void JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_endInflating 28 (JNIEnv *, jobject, jint); 29 30 /* 31 * Class: org_amse_ys_zip_DeflatingDecompressor 32 * Method: inflate 33 * Signature: (I[BII[B)J 34 */ 35 JNIEXPORT jlong JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_inflate 36 (JNIEnv *, jobject, jint, jbyteArray, jint, jint, jbyteArray); 37 38 #ifdef __cplusplus 39 } 40 #endif 41 #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:
1 /* 2 * Copyright (C) 2009-2013 Geometer Plus <contact@geometerplus.com> 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License as published by 6 * the Free Software Foundation; either version 2 of the License, or 7 * (at your option) any later version. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * GNU General Public License for more details. 13 * 14 * You should have received a copy of the GNU General Public License 15 * along with this program; if not, write to the Free Software 16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 17 * 02110-1301, USA. 18 */ 19 #include <string.h> 20 #include "zlib.h" 21 22 #include <new> 23 #include "jni.h" 24 #include "org_amse_ys_zip_DeflatingDecompressor.h" 25 26 #define SIZE 10 27 28 static z_stream* ourStreams[SIZE] = { 0 }; 29 30 extern "C" 31 JNIEXPORT jint JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_startInflating(JNIEnv *env, jobject thiz) { 32 int i; 33 for (i = 0; i < SIZE; ++i) { 34 if (ourStreams[i] == 0) { 35 ourStreams[i] = new z_stream; 36 memset(ourStreams[i], 0, sizeof(z_stream)); 37 inflateInit2(ourStreams[i], -MAX_WBITS); 38 return i; 39 } 40 } 41 return -1; 42 } 43 44 extern "C" 45 JNIEXPORT void JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_endInflating(JNIEnv *env, jobject thiz, jint inflatorId) { 46 if (inflatorId >= 0 && inflatorId < SIZE) { 47 inflateEnd(ourStreams[inflatorId]); 48 delete ourStreams[inflatorId]; 49 ourStreams[inflatorId] = 0; 50 } 51 } 52 53 // returns (endFlag << 32) + ((used inLength) << 16) + outLength 54 extern "C" 55 JNIEXPORT jlong JNICALL Java_org_amse_ys_zip_DeflatingDecompressor_inflate(JNIEnv *env, jobject thiz, jint inflatorId, jbyteArray in, jint inOffset, jint inLength, jbyteArray out) { 56 if (inflatorId < 0 || inflatorId >= SIZE) { 57 return -1; 58 } 59 z_stream *stream = ourStreams[inflatorId]; 60 if (stream == 0) { 61 return -2; 62 } 63 64 jbyte* inStart = env->GetByteArrayElements(in, 0); 65 jbyte* outStart = env->GetByteArrayElements(out, 0); 66 stream->next_in = (Bytef*)inStart + inOffset; 67 stream->avail_in = inLength; 68 stream->next_out = (Bytef*)outStart; 69 const int outLength = env->GetArrayLength(out); 70 stream->avail_out = outLength; 71 const int code = inflate(stream, Z_SYNC_FLUSH); 72 env->ReleaseByteArrayElements(in, inStart, 0); 73 env->ReleaseByteArrayElements(out, outStart, 0); 74 if (code == Z_OK || code == Z_STREAM_END) { 75 jlong result = ((inLength - stream->avail_in) << 16) + outLength - stream->avail_out; 76 if (code == Z_STREAM_END) { 77 result |= ((jlong)1) << 32; 78 } 79 return result; 80 } 81 return -1024 + code; 82 }
成功编译出DeflatingDecompressor.dll文件。
然后在的j2se工程的DeflatingDecompressor.java中使用
1 static { 2 System.loadLibrary("libs/DeflatingDecompressor"); 3 }
加载动态库，得到
1 Exception in thread "main" java.lang.UnsatisfiedLinkError: D:\Works\TextLayout\NewReaderSE\libs\DeflatingDecompressor.dll: Can't find dependent libraries 2 at java.lang.ClassLoader$NativeLibrary.load(Native Method) 3 at java.lang.ClassLoader.loadLibrary0(Unknown Source) 4 at java.lang.ClassLoader.loadLibrary(Unknown Source) 5 at java.lang.Runtime.loadLibrary0(Unknown Source) 6 at java.lang.System.loadLibrary(Unknown Source) 7 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
