聊聊maxwell的Scripting

序

本文主要研究一下maxwell的Scripting

Scripting

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/scripting/Scripting.java

public class Scripting {
    static final Logger LOGGER = LoggerFactory.getLogger(Scripting.class);

    private final ScriptObjectMirror processRowFunc, processHeartbeatFunc, processDDLFunc;

    private ScriptObjectMirror getFunc(ScriptEngine engine, String fName, String filename) {
        ScriptObjectMirror f = (ScriptObjectMirror) engine.get(fName);
        if ( f == null )
            return null;
        else if ( !f.isFunction() ) {
            throw new RuntimeException("Expected " + fName + " to be a function!");
        } else {
            LOGGER.info("using function " + fName + " from " + filename);
        }
        return f;
    }

    public Scripting(String filename) throws IOException, ScriptException, NoSuchMethodException {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("nashorn");

        String externJS = new String(Files.readAllBytes(Paths.get(filename)));
        engine.put("logger", LOGGER);
        engine.eval(externJS);

        processRowFunc = getFunc(engine, "process_row", filename);
        processHeartbeatFunc = getFunc(engine, "process_heartbeat", filename);
        processDDLFunc = getFunc(engine, "process_ddl", filename);

        if ( processRowFunc == null && processHeartbeatFunc == null && processDDLFunc == null )
            LOGGER.warn("expected " + filename + " to define at least one of: process_row,process_heartbeat,process_ddl");
    }

    public void invoke(RowMap row) {
        if ( row instanceof HeartbeatRowMap && processHeartbeatFunc != null )
            processHeartbeatFunc.call(null, new WrappedHeartbeatMap((HeartbeatRowMap) row));
        else if ( row instanceof DDLMap && processDDLFunc != null )
            processDDLFunc.call(null, new WrappedDDLMap((DDLMap) row));
        else if ( row instanceof RowMap && processRowFunc != null )
            processRowFunc.call(null, new WrappedRowMap(row));
    }

    private static ThreadLocal<ScriptEngine> stringifyEngineThreadLocal = ThreadLocal.withInitial(() -> {
        ScriptEngineManager manager = new ScriptEngineManager();
        return manager.getEngineByName("nashorn");
    });

    public static String stringify(ScriptObjectMirror mirror) throws ScriptException {
        ScriptObjectMirror json = (ScriptObjectMirror) stringifyEngineThreadLocal.get().eval("JSON");
        return (String) json.callMember("stringify", mirror);
    }
}

• Scripting定義了processRowFunc、processHeartbeatFunc、processDDLFunc屬性；其構造器接收filename參數，它建立ScriptEngineManager，而後獲取名爲nashorn的ScriptEngine，以後經過filename獲取externJS，並執行engine.eval(externJS)，以後經過getFunc方法初始化化processRowFunc、processHeartbeatFunc、processDDLFunc；其getFunc方法經過engine.get(fName)獲取ScriptObjectMirror；其invoke方法針對HeartbeatRowMap執行processHeartbeatFunc.call，針對DDLMap執行processDDLFunc.call，針對RowMap執行processRowFunc.call

MaxwellConfig

maxwell-1.25.1/src/main/java/com/zendesk/maxwell/MaxwellConfig.java

public class MaxwellConfig extends AbstractConfig {
    static final Logger LOGGER = LoggerFactory.getLogger(MaxwellConfig.class);

    //......

    public String javascriptFile;
    public Scripting scripting;

    //......

    public void validate() {
        validatePartitionBy();
        validateFilter();

        //......

        if ( this.javascriptFile != null ) {
            try {
                this.scripting = new Scripting(this.javascriptFile);
            } catch ( Exception e ) {
                LOGGER.error("Error setting up javascript: ", e);
                System.exit(1);
            }
        }
    }

    //......

}

• MaxwellConfig的validate方法在javascriptFile不爲null的時候會建立Scripting，若是出現異常則執行System.exit(1)

小結

Scripting定義了processRowFunc、processHeartbeatFunc、processDDLFunc屬性；其構造器接收filename參數，它建立ScriptEngineManager，而後獲取名爲nashorn的ScriptEngine，以後經過filename獲取externJS，並執行engine.eval(externJS)，以後經過getFunc方法初始化化processRowFunc、processHeartbeatFunc、processDDLFunc；其getFunc方法經過engine.get(fName)獲取ScriptObjectMirror；其invoke方法針對HeartbeatRowMap執行processHeartbeatFunc.call，針對DDLMap執行processDDLFunc.call，針對RowMap執行processRowFunc.call

doc

• Scripting