ClassPathScanner 实际上是dremio 基于配置+约定的类扫描处理，为了性能同时使用了开源的reflections 工具包
约定
主要扫描包含以下约定key 的类或者包
/** Configuration pathname to list of names of packages to scan for implementations. */
private static final String IMPLEMENTATIONS_SCAN_PACKAGES = "dremio.classpath.scanning.packages";
/** Configuration pathname to list of names of base classes to scan for implementations. */
private static final String IMPLEMENTATIONS_SCAN_CLASSES = "dremio.classpath.scanning.base.classes";
/** Configuration pathname to list of names of annotations to scan for. */
private static final String IMPLEMENTATIONS_SCAN_ANNOTATIONS = "dremio.classpath.scanning.annotations";
/** Configuration pathname to turn off build time caching. */
private static final String IMPLEMENTATIONS_SCAN_CACHE = "dremio.classpath.scanning.cache.enabled";
配置
基于了typesafe.config ，参考配置文件sabot-module.conf
dremio {classpath.scanning {
base.classes : ${?dremio.classpath.scanning.base.classes} [com.dremio.common.logical.data.LogicalOperator,
com.dremio.common.logical.FormatPluginConfig,
com.dremio.common.store.StoragePluginConfig,
com.dremio.service.Initializer
],
packages : ${?dremio.classpath.scanning.packages} [com.dremio.exec.store.mock,
com.dremio.common.logical,
com.dremio.exec.store.dfs,
com.dremio.exec.server.options,
com.dremio.plugins.mongo
]
},
memory: {debug.error_on_leak: true,
top.max: 1000000000000
}
}
参考使用
会返回一个ScanResult
public static ScanResult fromPrescan(SabotConfig config) {List<String> packagePrefixes = ClassPathScanner.getPackagePrefixes(config);
List<String> scannedBaseClasses = ClassPathScanner.getScannedBaseClasses(config);
List<String> scannedAnnotations = ClassPathScanner.getScannedAnnotations(config);
if (ClassPathScanner.isScanBuildTimeCacheEnabled(config)) {// scan only locations that have not been scanned yet
ScanResult runtimeScan = ClassPathScanner.scan(
NON_PRESCANNED_MARKED_PATHS,
packagePrefixes,
scannedBaseClasses,
scannedAnnotations,
PRESCANNED);
return runtimeScan.merge(PRESCANNED);
} else {// scan everything
return ClassPathScanner.scan(
ClassPathScanner.getMarkedPaths(),
packagePrefixes,
scannedBaseClasses,
scannedAnnotations,
ClassPathScanner.emptyResult());
}
}
说明
dremio 对于插件的加载就使用了动态创建以及类扫描的处理，灵活性还是很不错的
参考资料
common/src/main/java/com/dremio/common/scanner/ClassPathScanner.java
common/src/main/java/com/dremio/common/config/SabotConfig.java
https://github.com/ronmamo/reflections
