Cenotso 6安装 webplib 0.4.2库，使用java调用成功

1，关于webp

http://baike.baidu.com/view/4447461.htm

WebP是Google新推出的影像技术，它可让网页图档有效进行压缩，同时又不影响图片格式兼容与实际清晰度，进而让整体网页下载速度加快。
与JPEG相同，WebP是一种有损压缩利用预测编码技术。但谷歌表示，这种格式的主要优势在于高效率。他们发现，“在质量相同的情况下，
WebP格式图像的体积要比JPEG格式图像小40%。
目前, Google放出了WebP文件解码器(libvpx)和命令行工具(webpconv)，用于JPEG等格式图片与WebP格式之间的转换。

官方网站：
https://code.google.com/p/webp/
https://developers.google.com/speed/webp/

webp最新版本是 0.4.2 ，下载地址：

https://chromium.googlesource.com/webm/libwebp/+/0.4.2

http://downloads.webmproject.org/releases/webp/libwebp-0.4.2.tar.gz

https://chromium.googlesource.com/webm/libwebp/+archive/0.4.2.tar.gz

2，安装（按照0.4.0安装的）

解压缩：
tar -zxvf libwebp-0.4.0.tar.gz

进入文件：
cd libwebp-0.4.2/
安装编译环境（需要openjdk）：
yum install  autoconf gcc make java-1.6.0-openjdk java-1.6.0-openjdk-devel java-1.6.0-openjdk
./configure
make & make install
默认的安装目录： 

/usr/local/lib

3，编译javalib库 

调用webp需要使用swig ，跨语言调用框架。http://www.swig.org/
cd libwebp-0.4.2/swig/

openjdk安装目录为：/usr/lib/jvm/java-openjdk

所以编译命令为：

gcc -shared -fPIC -fno-strict-aliasing -O2 -I/usr/lib/jvm/java-openjdk/include -I/usr/lib/jvm/java-openjdk/include/linux  libwebp_java_wrap.c  -lwebp  -o /usr/local/lib/libwebp_jni.so

直接将so文件安装到/usr/local/lib

如果编译错误：（则openjdk安装目录有问题，重新安装）

 #include <jni.h>                 ^compilation terminated.

jni.h在目录：/usr/lib/jvm/java-openjdk/include

 #include "jni_md.h"                    ^compilation terminated.

jni_md.h在目录：/usr/lib/jvm/java-openjdk/include/linux

编写java代码：

import com.google.webp.libwebp;import java.lang.reflect.Method;public class libwebp_jni_example {  static {    System.out.println("###################");    System.out.println(System.getProperty("java.library.path"));    System.loadLibrary("webp_jni");  }  /**   * usage: java -cp libwebp.jar:. libwebp_jni_example   */  public static void main(String argv[]) {    final int version = libwebp.WebPGetDecoderVersion();    System.out.println("libwebp version: " + Integer.toHexString(version));    System.out.println("libwebp methods:");    final Method[] libwebpMethods = libwebp.class.getDeclaredMethods();    for (int i = 0; i < libwebpMethods.length; i++) {      System.out.println(libwebpMethods[i]);    }  }}

编译java代码：（检查libwebp.jar jar是否在当前目录）
javac libwebp_jni_example.java -cp libwebp.jar 

运行java代码：

java -cp libwebp.jar:. -Djava.library.path=/usr/local/lib libwebp_jni_example 

如果有问题：

Exception in thread "main" java.lang.UnsatisfiedLinkError: no webp_jni in java.library.path        at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1886)        at java.lang.Runtime.loadLibrary0(Runtime.java:849)        at java.lang.System.loadLibrary(System.java:1088)        at libwebp_jni_example.<clinit>(libwebp_jni_example.java:9)

说明/usr/local/lib没有libwebp_jni.so，检查是否编译so文件，文件大小是否正确。

如果有问题：

Exception in thread "main" java.lang.UnsatisfiedLinkError: /usr/local/lib/libwebp_jni.so: libwebp.so.5: cannot open shared object file: No such file or directory        at java.lang.ClassLoader$NativeLibrary.load(Native Method)        at java.lang.ClassLoader.loadLibrary1(ClassLoader.java:1965)        at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1890)        at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1880)        at java.lang.Runtime.loadLibrary0(Runtime.java:849)        at java.lang.System.loadLibrary(System.java:1088)        at libwebp_jni_example.<clinit>(libwebp_jni_example.java:9)

说明目录LD_LIBRARY_PATH和java.library.path目录不一致。或者libwebp.so文件有问题，比如大小为0，则可能编译有问题，目前在centos6编译成功。

则设置环境变量：export LD_LIBRARY_PATH=/usr/local/lib

/usr/local/lib目录下面文件如下：

-rw-r--r--. 1 root root 4412068 Feb  3 16:40 libwebp.a-rwxr-xr-x. 1 root root   37138 Feb  3 16:44 libwebp_jni.so-rwxr-xr-x. 1 root root     952 Feb  3 16:40 libwebp.lalrwxrwxrwx. 1 root root      16 Feb  3 16:40 libwebp.so -> libwebp.so.5.0.2lrwxrwxrwx. 1 root root      16 Feb  3 16:40 libwebp.so.5 -> libwebp.so.5.0.2-rwxr-xr-x. 1 root root 2389782 Feb  3 16:40 libwebp.so.5.0.2drwxr-xr-x. 2 root root      23 Feb  3 16:40 pkgconfig

4,如果都没有问题，则运行成功结果如下：

###################/usr/local/liblibwebp version: 400libwebp methods:public static int com.google.webp.libwebp.WebPGetDecoderVersion()public static byte[] com.google.webp.libwebp.WebPDecodeRGBA(byte[],long,int[],int[])public static byte[] com.google.webp.libwebp.WebPDecodeARGB(byte[],long,int[],int[])public static int com.google.webp.libwebp.WebPGetInfo(byte[],long,int[],int[])public static byte[] com.google.webp.libwebp.WebPDecodeRGB(byte[],long,int[],int[])public static byte[] com.google.webp.libwebp.WebPDecodeBGR(byte[],long,int[],int[])public static byte[] com.google.webp.libwebp.WebPDecodeBGRA(byte[],long,int[],int[])public static int com.google.webp.libwebp.WebPGetEncoderVersion()private static byte[] com.google.webp.libwebp.wrap_WebPEncodeRGB(byte[],int,int,int[],int,int,int,float)private static byte[] com.google.webp.libwebp.wrap_WebPEncodeBGR(byte[],int,int,int[],int,int,int,float)private static byte[] com.google.webp.libwebp.wrap_WebPEncodeRGBA(byte[],int,int,int[],int,int,int,float)private static byte[] com.google.webp.libwebp.wrap_WebPEncodeBGRA(byte[],int,int,int[],int,int,int,float)private static byte[] com.google.webp.libwebp.wrap_WebPEncodeLosslessRGB(byte[],int,int,int[],int,int,int)private static byte[] com.google.webp.libwebp.wrap_WebPEncodeLosslessBGR(byte[],int,int,int[],int,int,int)private static byte[] com.google.webp.libwebp.wrap_WebPEncodeLosslessRGBA(byte[],int,int,int[],int,int,int)private static byte[] com.google.webp.libwebp.wrap_WebPEncodeLosslessBGRA(byte[],int,int,int[],int,int,int)public static byte[] com.google.webp.libwebp.WebPEncodeRGB(byte[],int,int,int,float)public static byte[] com.google.webp.libwebp.WebPEncodeRGBA(byte[],int,int,int,float)public static byte[] com.google.webp.libwebp.WebPEncodeBGR(byte[],int,int,int,float)public static byte[] com.google.webp.libwebp.WebPEncodeBGRA(byte[],int,int,int,float)public static byte[] com.google.webp.libwebp.WebPEncodeLosslessRGB(byte[],int,int,int)public static byte[] com.google.webp.libwebp.WebPEncodeLosslessRGBA(byte[],int,int,int)public static byte[] com.google.webp.libwebp.WebPEncodeLosslessBGR(byte[],int,int,int)public static byte[] com.google.webp.libwebp.WebPEncodeLosslessBGRA(byte[],int,int,int)