1，关于webp
http://baike.baidu.com/view/4447461.htmWebP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 l ibwebp.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.la lrwxrwxrwx. 1 root root 16 Feb 3 16:40 libwebp.so -> libwebp.so.5.0.2 lrwxrwxrwx. 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.5.0.2 drwxr-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/lib libwebp version: 400 libwebp 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)
