最近在研究图计算相关技术，前一阶段学了Neo4j的知识，在学习的过程也对比一些其它的开源图数据库，如OrientDB，还有一些通用框架TinkerPop。
在OrientDB的对比学习过程中，希望首先把已有的数据导入到新的数据库中，还好OrientDB官方提供了Neo4j数据导入工具orientdb-neo4j-importer。然而一切皆有坑...
按照官方文档进行数据导入，执行命令：
sh orientdb-neo4j-importer-2.2.31/bin/orientdb-neo4j-importer.sh -neo4jdbdir ../graph.db/ -neo4jlibdir ../neo4jlib/
出现以下报错：
Exception in thread "main" java.lang.NoClassDefFoundError: com/orientechnologies/orient/core/OConstants
at com.orientechnologies.orient.neo4jimporter.ONeo4jImporterMain.main(ONeo4jImporterMain.java:15)
Caused by: java.lang.ClassNotFoundException: com.orientechnologies.orient.core.OConstants
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 1 more
尝试把importer/lib/orientdb-neo4j-importer-2.2.31.jar拷贝到orientdb安装目录的lib文件夹下，再次执行还是同样的报错。
查看源代码也没发现此处有问题，再通过sh打印详细信息发现环境变量ORIENTDB_HOME设置有问题，执行以下命令定义环境变量：
export ORIENTDB_HOME=/root/orientdb-community-importers-2.2.31
再次执行命令，顺利通过！
[root@datanode orientdb-community-importers-2.2.31]# sh -x orientdb-neo4j-importer-2.2.31/bin/orientdb-neo4j-importer.sh -neo4jdbdir ../graph.db/ -neo4jlibdir ../neo4jlib/ + PRG=orientdb-neo4j-importer-2.2.31/bin/orientdb-neo4j-importer.sh + '[' -h orientdb-neo4j-importer-2.2.31/bin/orientdb-neo4j-importer.sh ']' ++ dirname orientdb-neo4j-importer-2.2.31/bin/orientdb-neo4j-importer.sh + PRGDIR=orientdb-neo4j-importer-2.2.31/bin + '[' -f /root/orientdb-community-importers-2.2.31/lib/orientdb-neo4j-importer-2.2.31.jar ']' + export ORIENTDB_HOME + '[' -f /usr/java/jdk1.8.0_91/bin/java ']' + JAVA=/usr/java/jdk1.8.0_91/bin/java + export JAVA + LOG_FILE=/root/orientdb-community-importers-2.2.31/config/orientdb-neo4j-importer-log.properties + JAVA_MAX_DIRECT=-XX:MaxDirectMemorySize=512g + JAVA_OPTS_SCRIPT='-XX:MaxDirectMemorySize=512g -Djava.util.logging.config.file=/root/orientdb-community-importers-2.2.31/config/orientdb-neo4j-importer-log.properties' + ARGS= + for var in '"$@"' + ARGS=' -neo4jdbdir' + for var in '"$@"' + ARGS=' -neo4jdbdir ../graph.db/' + for var in '"$@"' + ARGS=' -neo4jdbdir ../graph.db/ -neo4jlibdir' + for var in '"$@"' + ARGS=' -neo4jdbdir ../graph.db/ -neo4jlibdir ../neo4jlib/' + [[ 4 -gt 1 ]] + key=-neo4jdbdir + case $key in + shift + [[ 3 -gt 1 ]] + key=../graph.db/ + case $key in + shift + [[ 2 -gt 1 ]] + key=-neo4jlibdir + case $key in + NEO4JLIB=../neo4jlib/ + shift + shift + [[ 0 -gt 1 ]] + exec /usr/java/jdk1.8.0_91/bin/java -client -cp '../neo4jlib//*:/root/orientdb-community-importers-2.2.31/lib/*' -XX:MaxDirectMemorySize=512g -Djava.util.logging.config.file=/root/orientdb-community-importers-2.2.31/config/orientdb-neo4j-importer-log.properties com.orientechnologies.orient.neo4jimporter.ONeo4jImporterMain -neo4jdbdir ../graph.db/ -neo4jlibdir ../neo4jlib/ Neo4j to OrientDB Importer v.2.2.31 (build 285537d2767275f460df32c6a3be01bfff6a517c,branch 2.2.x) - Copyrights (c) 2016 OrientDB LTD WARNING: 'o' option not found. Defaulting to 'false'. WARNING: 'i' option not found. Defaulting to 'false'. WARNING: 'odbdir' option not found. Defaulting to '/root/databases/neo4j_import'. Please make sure that there are no running servers on: '../graph.db' (Neo4j) and: '/root/databases/neo4j_import' (OrientDB) Initializing Neo4j...Done Initializing OrientDB...Done Importing Neo4j database: '../graph.db' into OrientDB database: '/root/databases/neo4j_import' Getting all Nodes from Neo4j and creating corresponding Vertices in OrientDB... 4 OrientDB Vertices have been created (100% done) Done Creating internal Indices on properties 'Neo4jNodeID' & 'Neo4jLabelList' on all OrientDB Vertices Classes... 4 OrientDB Indices have been created (100% done) Done Getting all Relationships from Neo4j and creating corresponding Edges in OrientDB... 2 OrientDB Edges have been created (100% done) Done Getting Constraints from Neo4j and creating corresponding ones in OrientDB... 0 OrientDB UNIQUE Indices have been created Done Getting Indices from Neo4j and creating corresponding ones in OrientDB... 0 OrientDB Indices have been created Done Import completed! Shutting down OrientDB...Done Shutting down Neo4j...Done =============== Import Summary: =============== - Found Neo4j Nodes : 4 -- With at least one Label : 4 --- With multiple Labels : 0 -- Without Labels : 0 - Imported OrientDB Vertices : 4 (100%) - Found Neo4j Relationships : 2 - Imported OrientDB Edges : 2 (100%) - Found Neo4j Constraints : 0 - Imported OrientDB Constraints (UNIQUE Indices created) : 0 - NOT UNIQUE Indices created due to failure in creating UNIQUE Indices : 0 - Found Neo4j (non-constraint) Indices : 0 - Imported OrientDB Indices : 0 - Additional internal Indices created : 4 - Total Import time: : 6 seconds -- Initialization time : 5 seconds -- Time to Import Nodes : 0 seconds (35.4 nodes/sec) -- Time to Import Relationships : 0 seconds (22.47 rels/sec) -- Time to Import Constraints and Indices : 0 seconds (0 indices/sec) -- Time to Create Internal Indices (on vertex properties 'Neo4jNodeID' & 'Neo4jLabelList') : 1 seconds (7.01 indices/sec)
以为一切搞定，启动OrientDB数据库，并没有看到新导入的数据库... 再仔细查看发现没有添加选项-odbdir（但是默认值应该是DB_HOME/databases/neo4j_import，不知道为何没有生效...），数据库导入到其它路径下，拷贝过来后可以正常使用了。
（如图，neo4j_import数据库）