org.apache.nutch.indexer.replace.FieldReplacer.java Source code

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Here is the source code for org.apache.nutch.indexer.replace.FieldReplacer.java

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/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.nutch.indexer.replace;

import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * POJO to store a filename, its match pattern and its replacement string.
 *
 * A checkAndReplace method is provided where you can simultaneously check if
 * the field matches this replacer and if the pattern matches your field value.
 *
 * @author Peter Ciuffetti
 */
public class FieldReplacer {

    private static final Log LOG = LogFactory.getLog(FieldReplacer.class.getName());

    private final String fieldName;
    private final String toFieldName;
    private final Pattern pattern;
    private final String replacement;
    private boolean isValid;

    /**
     * Create a FieldReplacer for a field.
     *
     * Any pattern exceptions are caught within this constructor and the object is
     * marked inValid. The error will be logged. This prevents this caller from
     * attempting invalid replacements.
     *
     * @param fieldName
     *          the name of the source field to operate on. Required.
     * @param toFieldName
     *          the name of the target field. Required.
     * @param pattern
     *          the pattern the field must match. Required.
     * @param replacement
     *          the replacement string
     * @param flags
     *          the Pattern flags value, or null if no flags are needed
     */
    public FieldReplacer(String fieldName, String toFieldName, String pattern, String replacement, Integer flags) {

        this.isValid = true;
        // Must have a non-empty field name and pattern.
        if (fieldName == null || fieldName.trim().length() == 0) {
            LOG.error("Empty fieldName provided, FieldReplacer marked invalid.");
            this.isValid = false;
        }
        if (pattern == null || pattern.trim().length() == 0) {
            LOG.error("Empty pattern for field " + fieldName + "provided, FieldReplacer marked invalid.");
            this.isValid = false;
        }

        if (replacement == null) {
            this.replacement = "";
        } else {
            this.replacement = replacement;
        }

        this.fieldName = fieldName.trim();
        this.toFieldName = toFieldName.trim();

        if (this.isValid) {
            LOG.info("Compiling pattern " + pattern + " for field " + fieldName);
            Pattern myPattern = null;
            try {
                if (flags != null) {
                    myPattern = Pattern.compile(pattern, flags);
                } else {
                    myPattern = Pattern.compile(pattern);
                }
            } catch (PatternSyntaxException e) {
                LOG.error("Pattern " + pattern + " for field " + fieldName + " failed to compile: " + e.toString());
                this.isValid = false;
            }
            this.pattern = myPattern;
        } else {
            this.pattern = null;
        }
    }

    /**
     * Field replacer with the input and output field the same.
     *
     * @param fieldName
     * @param pattern
     * @param replacement
     * @param flags
     */
    public FieldReplacer(String fieldName, String pattern, String replacement, Integer flags) {
        this(fieldName, fieldName, pattern, replacement, flags);
    }

    public String getFieldName() {
        return this.fieldName;
    }

    public String getToFieldName() {
        return this.toFieldName;
    }

    public Pattern getPattern() {
        return this.pattern;
    }

    public String getReplacement() {
        return this.replacement;
    }

    /**
     * Does this FieldReplacer have a valid fieldname and pattern?
     *
     * @return
     */
    public boolean isValid() {
        return this.isValid;
    }

    /**
     * Return the replacement value for a field value.
     *
     * This does not check for a matching field; the caller must decide if this
     * FieldReplacer should operate on this value by checking getFieldName().
     *
     * The method returns the value with the replacement. If the value returned is
     * not different then eiher the pattern didn't match or the replacement was a
     * no-op.
     *
     * @param value
     * @return
     */
    public String replace(String value) {
        if (this.isValid) {
            return this.pattern.matcher(value).replaceAll(replacement);
        } else {
            return value;
        }
    }

    /**
     * Return a replacement value for a field.
     *
     * This is designed to fail fast and trigger a replacement only when
     * necessary. If this method returns null, either the field does not match or
     * the value does not match the pattern (or possibly the pattern is invalid).
     *
     * So only if the method returns a non-null value will you need to replace the
     * value for the field.
     *
     * @param fieldName
     *          the name of the field you are checking
     * @param value
     *          the value of the field you are checking
     * @return a replacement value. If null, either the field does not match or
     *         the value does not match.
     */
    public String checkAndReplace(String fieldName, String value) {
        if (this.fieldName.equals(fieldName)) {
            if (value != null && value.length() > 0) {
                if (this.isValid) {
                    Matcher m = this.pattern.matcher(value);
                    if (m.find()) {
                        return m.replaceAll(this.replacement);
                    }
                }
            }
        }
        return null;
    }
}