如何在java程序中引入neo4j数据库

neo4j采纳java语言开发，如果我们要在java程序中以内嵌方式应用neo4j，只需导入neo4j的对应包即可。

首先，我们来创建一个maven项目并改动pom.xml添加对neo4j的依附。

<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 "><modelVersion>4.0.0</modelVersion><groupId>neo4j-learn</groupId><artifactId>neo4j-learn</artifactId><version>1.0-SNAPSHOT</version><dependencies><dependency><groupId>org.neo4j</groupId><artifactId>neo4j</artifactId><version>1.9.4</version></dependency></dependencies></project>

然后，我们在项目中创建一个neo4j.properties（数据库的配置文件）文件和一个java类（调用数据库）。

neo4j.properties

# Default values for the low-level graph engine #neostore.nodestore.db.mapped_memory=25M #neostore.relationshipstore.db.mapped_memory=50M #neostore.propertystore.db.mapped_memory=90M #neostore.propertystore.db.strings.mapped_memory=130M #neostore.propertystore.db.arrays.mapped_memory=130M # Autoindexing # Enable auto-indexing for nodes, default is false #node_auto_indexing=true # The node property keys to be auto-indexed, if enabled #node_keys_indexable=name,age # Enable auto-indexing for relationships, default is false #relationship_auto_indexing=true # The relationship property keys to be auto-indexed, if enabled #relationship_keys_indexable=name,age # Keep logical logs, needed for online backups to work keep_logical_logs=true # Enable online backups to be taken from this database. online_backup_enabled=true # Uncomment and specify these lines for running Neo4j in High Availability mode. # ha.server_id is a unique integer for each instance of the Neo4j database in the cluster. # (as opposed to the coordinator instance IDs) # example: ha.server_id=1 #ha.server_id= # ha.coordinators is a comma-separated list (without spaces) of the host:port of where to # find one or more of the Neo4j coordinator servers. # Avoid localhost due to IP resolution issues on some systems. # example: ha.coordinators=localhost:2181,1.2.3.4:4321 #ha.coordinators=localhost:2181 # You can also, optionally, configure the ha.cluster_name. This is the name of the cluster this # instance is supposed to join. Accepted characters are alphabetical, numerical, dot and dash. # This configuration is useful if you have multiple Neo4j HA clusters managed by the same # Coordinator cluster. # Example: ha.cluster_name = my.neo4j.ha.cluster #ha.cluster_name = # IP and port for this instance to bind to to communicate data with the # other neo4j instances in the cluster. This is broadcasted to the other # cluster members, so different members can have different communication ports. # Optional if the members are on different machines so the IP is different for every member. #ha.server = localhost:6001 # The interval at which slaves will pull updates from the master. Comment out # the option to disable periodic pulling of updates. Unit is seconds. ha.pull_interval = 10 # The session timeout for the zookeeper client. Lower values make new master # election happen closer to the master loosing connection but also more sensitive # to zookeeper quorum hiccups. If experiencing master switches without reason # consider increasing this value. Unit is seconds #ha.zk_session_timeout = 5 # Amount of slaves the master will try to push a transaction to upon commit (default is 1). # The master will optimistically continue and not fail the transaction even if it fails to # reach the push factor. Setting this to 0 will increase write performance when writing # through master but could potentially lead to branched data (or loss of transaction) # if the master goes down. #ha.tx_push_factor=1 # Strategy the master will use when pushing data to slaves (if the push factor is greater than 0). # There are two options available "fixed" (default) or "round_robin". Fixed will start by # pushing to slaves ordered by server id (highest first) improving performance since the # slaves only have to cache up one transaction at a time. #ha.tx_push_strategy=fixed # Enable this to be able to upgrade a store from 1.4 ->1.5 or 1.4 ->1.6 #allow_store_upgrade=true # Enable this to specify a parser other than the default one. 1.5, 1.6, 1.7 are available #cypher_parser_version=1.6

java文件（neo4j示例文件改动而来）

Neo4J的安装使用非常简单。下载一个稳定版本，解压，运行Neo4j.bat（windows版本） 即可。下载地址http://www.neo4j.org/download ， 目前比较好用的稳定版本是1.9.1。

然后可以访问WEB管理界面，地址：http://localhost:7474/webadmin

Neo4J的使用方式包括：

1）可以写程序，添加，更新，用JAVA，Python，PHP, .NET等语言都可以实现。

2）可以用命令行，添加，更新，查看，Neo4J提供基于WEB的执行界面，提供类SQL语言执行，这些语言包括Cypher，Gremlin等。

如下图：

3）可以基于Neo4J提供的WEB UI界面添加，更新节点和关系，如下：

4) 可以使用附加工具（ETL）导入数据。也可以从关系数据库中导入数据。

APOC是Neo4j 3.3版本推出时正式推荐的一个Java用户扩展过程包，里面包含丰富的函数和过程，作为对Cypher所不能提供的复杂图算法和数据 *** 作功能的补充，APOC还具有使用灵活、高性能等优势。

APOC的安装：

启动neo4j，运行如下cypher，判断类型

return apoc.meta.type('hello') 返回 STRING ，注意返回值都是大写。

return apoc.meta.type(["hello", "world"]) 返回 LIST

create(n:Fruit{name:'apple', color:['red', 'green']})

match(n:Fruit) return apoc.meta.type(n.color) 返回 STRING[]

return apoc.meta.type(1) 返回 INTEGER

Tip：

如果出现上面的错误，是因为安装的时候没有修改配置文件

应用：

对Neo4j中的数据进行修改，将字符串数组压平为字符串，但是该属性中既有字符串，又有字符串数组，需要判断该属性是哪种数据类型，进行相应的 *** 作。Cypher自带的 size 函数，对于字符串返回的是字符串的长度，对于集合类型返回的是其中的元素个数。例如：

在前边 create(n:Fruit{name:'apple', color:['red', 'green']}) 的基础上 create(:Fruit{name:'banana', color:'yellow'})

查询 match(n:Fruit) return n.name, size(n.color)

使用apoc中的函数： apoc.meta.type()

查询 match(n:Fruit) return n.name, apoc.meta.type(n.color)

查找所有color属性为字符串数组类型的节点：

match(n:Fruit) where apoc.meta.type(n.color) = 'STRING[]' return n.name, n.color

此外 apoc.meta.typeName() 函数和 apoc.meta.type() 相同

压平：

对数据类型为字符串数组的属性值进行压平，中间用逗号隔开，逗号后边跟一个空格，末尾不带有括号。

create(n:Fruit{name:'grape', color:['purple', 'green', 'white']})

match(n:Fruit) where apoc.meta.type(n.color) = 'STRING[]' return substring(reduce(s='', x IN n.color | s + ', ' + x), 2)

这里使用到了Cypher自带的 reduce 函数。

若将color属性为字符串数组的，设置为字符串数组中的第一个元素：

match(n:Fruit) where apoc.meta.type(n.color) = 'STRING[]' set n.color = n.color[0]

连接：

参考：

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