com.ibm.jaql.lang.expr.hadoop.ReadConfExpr.java Source code

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Here is the source code for com.ibm.jaql.lang.expr.hadoop.ReadConfExpr.java

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/*
 * Copyright (C) IBM Corp. 2008.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.ibm.jaql.lang.expr.hadoop;

import org.apache.hadoop.mapred.JobConf;

import com.ibm.jaql.io.hadoop.Globals;
import com.ibm.jaql.json.type.JsonString;
import com.ibm.jaql.json.type.JsonValue;
import com.ibm.jaql.lang.core.Context;
import com.ibm.jaql.lang.expr.core.Expr;
import com.ibm.jaql.lang.expr.function.DefaultBuiltInFunctionDescriptor;

/**
 * @jaqlDescption read a value from jaql's current Hadoop JobConf
 * Usage:
 * string readConf(string name, string? dflt);
 * 
 * Jaql stores the JobConf that is associated with the current
 * map-reduce job. This function reads name from this JobConf and
 * returns its value, otherwise it returns the dflt value.
 * 
 */
public class ReadConfExpr extends Expr {
    public static class Descriptor extends DefaultBuiltInFunctionDescriptor.Par12 {
        public Descriptor() {
            super("readConf", ReadConfExpr.class);
        }
    }

    /**
     * @param exprs
     */
    public ReadConfExpr(Expr[] exprs) {
        super(exprs);
    }

    /*
     * (non-Javadoc)
     * 
     * @see com.ibm.jaql.lang.expr.core.Expr#eval(com.ibm.jaql.lang.core.Context)
     */
    @Override
    public JsonValue eval(Context context) throws Exception {
        JobConf conf = Globals.getJobConf();
        if (conf == null) {
            conf = new JobConf();
            Globals.setJobConf(conf);
        }

        JsonString name = (JsonString) exprs[0].eval(context);
        String val = conf.get(name.toString());
        JsonValue dflt = null;
        if (val == null) {
            dflt = exprs[1].eval(context);
            return dflt;
        }

        return new JsonString(val);
    }
}