HugeGraph是一個Java語言實現的開源圖數據庫,內置支持多種後端存儲(Cassandra、RocksDB等),此外還支持通過插件的方式擴展存儲後端。插件實現者無需更改HugeGraph本身源代碼,插件使用者無需關注代碼細節,就能輕鬆增加插件擴展功能。這篇文章主要講述了HugeGraph擴展自定義插件的流程。
可擴展維度
目前插件方式提供如下幾個維度的擴展項:
- 後端存儲:HugeGraph支持多種內置存儲後端,也允許用戶無需更改現有源碼的情況下擴展自定義後端。
- 系列化器:配合自定義後端實現系列化器,或者擴展內置後端的系列化器。
- 自定義配置項:配合自定義插件擴展配置項。
- 分詞器:HugeGraph支持全文檢索,全文檢索功能涉及到各語言分詞,目前已內置8種中文分詞器,也允許用戶無需更改現有源碼的情況下擴展自定義分詞器。
插件實現機制
- HugeGraph提供插件接口HugeGraphPlugin,通過Java SPI機制支持插件化
- HugeGraph提供了4個擴展項註冊函數:
registerOptions()
、registerBackend()
、registerSerializer()
、registerAnalyzer()
- 插件實現者實現相應的Options、Backend、Serializer或Analyzer的接口
- 插件實現者實現HugeGraphPlugin接口的
register()
方法,在register()
中調用上述第2步中的函數,來註冊第3步列出的具體實現類,並打成jar包 - 插件使用者將jar包放在HugeGraph-Server安裝目錄的
plugins
目錄下,修改相關配置項爲插件自定義值,重啓即可生效
插件實現流程實例
1 新建一個maven項目
1.1 項目名稱取名:hugegraph-plugin-demo
1.2 添加hugegraph-core
Jar包依賴
maven pom.xml詳細內容如下:
<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.baidu.hugegraph</groupId>
<artifactId>hugegraph-plugin-demo</artifactId>
<version>1.0.0</version>
<packaging>jar</packaging>
<name>hugegraph-plugin-demo</name>
<dependencies>
<dependency>
<groupId>com.baidu.hugegraph</groupId>
<artifactId>hugegraph-core</artifactId>
<version>${project.version}</version>
</dependency>
</dependencies>
</project>
2 實現擴展功能
擴展功能一般包括:擴展自定義後端存儲(下文2.1講述)和擴展自定義分詞器(下文2.2講述)。插件實現者關注其中之一即可,若有需要當然也可兩者同時進行擴展,或者只擴展下文2.1.3所述系列化器等。
2.1 擴展自定義後端
2.1.1 實現接口BackendStoreProvider
- 可實現接口:
com.baidu.hugegraph.backend.store.BackendStoreProvider
- 或者繼承抽象類:
com.baidu.hugegraph.backend.store.AbstractBackendStoreProvider
以RocksDB後端RocksDBStoreProvider爲例:
public class RocksDBStoreProvider extends AbstractBackendStoreProvider {
protected String database() {
return this.graph().toLowerCase();
}
@Override
protected BackendStore newSchemaStore(String store) {
return new RocksDBSchemaStore(this, this.database(), store);
}
@Override
protected BackendStore newGraphStore(String store) {
return new RocksDBGraphStore(this, this.database(), store);
}
@Override
public String type() {
return "rocksdb";
}
@Override
public String version() {
return "1.0";
}
}
2.1.2 實現接口BackendStore
BackendStore接口定義如下:
public interface BackendStore {
// Store name
public String store();
// Database name
public String database();
// Get the parent provider
public BackendStoreProvider provider();
// Open/close database
public void open(HugeConfig config);
public void close();
// Initialize/clear database
public void init();
public void clear();
// Add/delete data
public void mutate(BackendMutation mutation);
// Query data
public Iterator<BackendEntry> query(Query query);
// Transaction
public void beginTx();
public void commitTx();
public void rollbackTx();
// Get metadata by key
public <R> R metadata(HugeType type, String meta, Object[] args);
// Backend features
public BackendFeatures features();
// Generate an id for a specific type
public Id nextId(HugeType type);
}
2.1.3 擴展自定義系列化器
系列化器必須繼承抽象類:com.baidu.hugegraph.backend.serializer.AbstractSerializer
(implements GraphSerializer, SchemaSerializer
)
主要接口的定義如下:
public interface GraphSerializer {
public BackendEntry writeVertex(HugeVertex vertex);
public BackendEntry writeVertexProperty(HugeVertexProperty<?> prop);
public HugeVertex readVertex(HugeGraph graph, BackendEntry entry);
public BackendEntry writeEdge(HugeEdge edge);
public BackendEntry writeEdgeProperty(HugeEdgeProperty<?> prop);
public HugeEdge readEdge(HugeGraph graph, BackendEntry entry);
public BackendEntry writeIndex(HugeIndex index);
public HugeIndex readIndex(HugeGraph graph, ConditionQuery query, BackendEntry entry);
public BackendEntry writeId(HugeType type, Id id);
public Query writeQuery(Query query);
}
public interface SchemaSerializer {
public BackendEntry writeVertexLabel(VertexLabel vertexLabel);
public VertexLabel readVertexLabel(HugeGraph graph, BackendEntry entry);
public BackendEntry writeEdgeLabel(EdgeLabel edgeLabel);
public EdgeLabel readEdgeLabel(HugeGraph graph, BackendEntry entry);
public BackendEntry writePropertyKey(PropertyKey propertyKey);
public PropertyKey readPropertyKey(HugeGraph graph, BackendEntry entry);
public BackendEntry writeIndexLabel(IndexLabel indexLabel);
public IndexLabel readIndexLabel(HugeGraph graph, BackendEntry entry);
}
2.1.4 擴展自定義配置項
增加自定義後端時,可能需要增加新的配置項,實現流程主要包括:
- 增加配置項容器類,並實現接口
com.baidu.hugegraph.config.OptionHolder
- 提供單例方法
public static OptionHolder instance()
,並在對象初始化時調用方法OptionHolder.registerOptions()
- 增加配置項聲明,單值配置項類型爲
ConfigOption
、多值配置項類型爲ConfigListOption
以RocksDB配置項定義爲例:
public class RocksDBOptions extends OptionHolder {
private RocksDBOptions() {
super();
}
private static volatile RocksDBOptions instance;
public static synchronized RocksDBOptions instance() {
if (instance == null) {
instance = new RocksDBOptions();
instance.registerOptions();
}
return instance;
}
public static final ConfigOption<String> DATA_PATH =
new ConfigOption<>(
"rocksdb.data_path",
"The path for storing data of RocksDB.",
disallowEmpty(),
"rocksdb-data"
);
public static final ConfigOption<String> WAL_PATH =
new ConfigOption<>(
"rocksdb.wal_path",
"The path for storing WAL of RocksDB.",
disallowEmpty(),
"rocksdb-data"
);
public static final ConfigListOption<String> DATA_DISKS =
new ConfigListOption<>(
"rocksdb.data_disks",
false,
"The optimized disks for storing data of RocksDB. " +
"The format of each element: `STORE/TABLE: /path/to/disk`." +
"Allowed keys are [graph/vertex, graph/edge_out, graph/edge_in, " +
"graph/secondary_index, graph/range_index]",
null,
String.class,
ImmutableList.of()
);
}
2.2 擴展自定義分詞器
分詞器需要實現接口com.baidu.hugegraph.analyzer.Analyzer
,以實現一個SpaceAnalyzer空格分詞器爲例。
package com.baidu.hugegraph.plugin;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
import com.baidu.hugegraph.analyzer.Analyzer;
public class SpaceAnalyzer implements Analyzer {
@Override
public Set<String> segment(String text) {
return new HashSet<>(Arrays.asList(text.split(" ")));
}
}
3 實現插件接口,並進行註冊
插件註冊入口爲HugeGraphPlugin.register()
,自定義插件必須實現該接口方法,在其內部註冊上述定義好的擴展項。
接口com.baidu.hugegraph.plugin.HugeGraphPlugin
定義如下:
public interface HugeGraphPlugin {
public String name();
public void register();
public String supportsMinVersion();
public String supportsMaxVersion();
}
並且HugeGraphPlugin提供了4個靜態方法用於註冊擴展項:
- registerOptions(String name, String classPath):註冊配置項
- registerBackend(String name, String classPath):註冊後端(BackendStoreProvider)
- registerSerializer(String name, String classPath):註冊系列化器
- registerAnalyzer(String name, String classPath):註冊分詞器
下面以註冊SpaceAnalyzer分詞器爲例:
package com.baidu.hugegraph.plugin;
public class DemoPlugin implements HugeGraphPlugin {
@Override
public String name() {
return "demo";
}
@Override
public void register() {
HugeGraphPlugin.registerAnalyzer("demo", SpaceAnalyzer.class.getName());
}
}
4 配置SPI入口
- 確保services目錄存在:hugegraph-plugin-demo/resources/META-INF/services
- 在services目錄下建立文本文件:com.baidu.hugegraph.plugin.HugeGraphPlugin
- 文件內容如下:com.baidu.hugegraph.plugin.DemoPlugin
5 打Jar包
通過maven打包,在項目目錄下執行命令mvn package
,在target目錄下會生成Jar包文件。
使用插件時將該Jar包拷到plugins
目錄,重啓服務即可生效。
HugeGraph擴展Stanford分詞器完整示例: https://github.com/hugegraph/hugegraph-plugin-stanford-analyzer
HugeGraph GitHub地址: https://github.com/hugegraph/hugegraph