Hadoop通过C的API访问HDFS

在通过Hadoop的C的API 访问HDFS的时候，编译和运行出现了不少问题，在这边，做个总结吧：

系统：Ubuntu11.04，Hadoop-0.20.203.0

样例代码就是参考官方文档中提供到：

#include "hdfs.h"

int main(int argc, char **argv) {

hdfsFS fs = hdfsConnect("default", 0);
const char* writePath = "/tmp/testfile.txt";
hdfsFile writeFile = hdfsOpenFile(fs, writePath, O_WRONLY|O_CREAT, 0, 0, 0);
if(!writeFile) {
fprintf(stderr, "Failed to open %s for writing!\n", writePath);
exit(-1);
}
char* buffer = "Hello, World!";
tSize num_written_bytes = hdfsWrite(fs, writeFile, (void*)buffer, strlen(buffer)+1);
if (hdfsFlush(fs, writeFile)) {
fprintf(stderr, "Failed to 'flush' %s\n", writePath);
exit(-1);
}
hdfsCloseFile(fs, writeFile);
}

编译：官网这样描述

See the Makefile for hdfs_test.c in the libhdfs source directory (${HADOOP_HOME}/src/c++/libhdfs/Makefile) or something like:

gcc above_sample.c -I${HADOOP_HOME}/src/c++/libhdfs -L${HADOOP_HOME}/libhdfs -lhdfs -o above_sample

但是我两个方法都试了，不行，后面发现原来是要少了：

LIB = -L$(HADOOP_INSTALL)/c++/Linux-i386-32/lib/
libjvm=/usr/lib/jvm/java-6-openjdk/jre/lib/i386/client/libjvm.so

所以完整到makefile就是：

HADOOP_INSTALL=/home/fzuir/hadoop-0.20.203.0
PLATFORM=Linux-i386-32
JAVA_HOME=/usr/lib/jvm/java-6-openjdk/
CPPFLAGS= -I$(HADOOP_INSTALL)/src/c++/libhdfs
LIB = -L$(HADOOP_INSTALL)/c++/Linux-i386-32/lib/
libjvm=/usr/lib/jvm/java-6-openjdk/jre/lib/i386/client/libjvm.soLDFLAGS += -lhdfs

testHdfs: testHdfs.c
gcc testHdfs.c  $(CPPFLAGS) $(LIB) $(LDFLAGS) $(libjvm) -o testHdfs

clean:
rm testHdfs

好了，编译通过，但是运行的时候出现以下错误信息：

1.

./testHdfs: error while loading shared libraries: xxx.so.0:cannot open shared object file: No such file or directory

解决方法：把xxx.so.0所在的目录添加到/etc/ld.so.conf中，然后/sbin/ldconfig –v下就可以了。

2.

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/configuration/Configuration

...

Call to org.apache.hadoop.fs.Filesystem::get(URI, Configuration) failed!

Exception in thread "main" java.lang.NullPointerException

Call to get configuration object from filesystem failed!

解决方法，修改/etc/profile,添加相应的CLASSPATH：

HADOOP_HOME=/home/fzuir/hadoop-0.20.203.0
export PATH=$HADOOP_HOME/bin:$PATH
export CLASSPATH=.:$HADOOP_HOME/lib/commons-lang-2.4.jar:$HADOOP_HOME/hadoop-cor
e-1.0.1.jar:$HADOOP_HOME/lib/commons-logging-api-1.0.4.jar:$HADOOP_HOME/lib/comm
ons-configuration-1.6.jar:$JAVA_HOME/lib:$JRE_HOME/lib:$HADOOP_HOME/contrib/stre
aming/hadoop-streaming-1.0.1.jar:$CLASSPATH

最后，恭喜你，问题解决了。