org.apache.kafka.streams.kstream.Printed Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of kafka-streams Show documentation
There is a newer version: 3.8.0
/*
 * 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.kafka.streams.kstream;

import org.apache.kafka.common.utils.Utils;
import org.apache.kafka.streams.errors.TopologyException;

import java.io.IOException;
import java.io.OutputStream;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Objects;

/**
 * An object to define the options used when printing a {@link KStream}.
 *
 * @param  key type
 * @param  value type
 * @see KStream#print(Printed)
 */
public class Printed implements NamedOperation> {
    protected final OutputStream outputStream;
    protected String label;
    protected String processorName;
    protected KeyValueMapper mapper =
        (KeyValueMapper) (key, value) -> String.format("%s, %s", key, value);

    private Printed(final OutputStream outputStream) {
        this.outputStream = outputStream;
    }

    /**
     * Copy constructor.
     * @param printed   instance of {@link Printed} to copy
     */
    protected Printed(final Printed printed) {
        this.outputStream = printed.outputStream;
        this.label = printed.label;
        this.mapper = printed.mapper;
        this.processorName = printed.processorName;
    }

    /**
     * Print the records of a {@link KStream} to a file.
     *
     * @param filePath path of the file
     * @param       key type
     * @param       value type
     * @return a new Printed instance
     */
    public static  Printed toFile(final String filePath) {
        Objects.requireNonNull(filePath, "filePath can't be null");
        if (Utils.isBlank(filePath)) {
            throw new TopologyException("filePath can't be an empty string");
        }
        try {
            return new Printed<>(Files.newOutputStream(Paths.get(filePath)));
        } catch (final IOException e) {
            throw new TopologyException("Unable to write stream to file at [" + filePath + "] " + e.getMessage());
        }
    }

    /**
     * Print the records of a {@link KStream} to system out.
     *
     * @param  key type
     * @param  value type
     * @return a new Printed instance
     */
    public static  Printed toSysOut() {
        return new Printed<>(System.out);
    }

    /**
     * Print the records of a {@link KStream} with the provided label.
     *
     * @param label label to use
     * @return this
     */
    public Printed withLabel(final String label) {
        Objects.requireNonNull(label, "label can't be null");
        this.label = label;
        return this;
    }

    /**
     * Print the records of a {@link KStream} with the provided {@link KeyValueMapper}
     * The provided KeyValueMapper's mapped value type must be {@code String}.
     * 
     * The example below shows how to customize output data.
     * 
{@code
     * final KeyValueMapper mapper = new KeyValueMapper() {
     *     public String apply(Integer key, String value) {
     *         return String.format("(%d, %s)", key, value);
     *     }
     * };
     * }
     *
     * Implementors will need to override {@code toString()} for keys and values that are not of type {@link String},
     * {@link Integer} etc. to get meaningful information.
     *
     * @param mapper mapper to use
     * @return this
     */
    public Printed withKeyValueMapper(final KeyValueMapper mapper) {
        Objects.requireNonNull(mapper, "mapper can't be null");
        this.mapper = mapper;
        return this;
    }

    /**
     * Print the records of a {@link KStream} with provided processor name.
     *
     * @param processorName the processor name to be used. If {@code null} a default processor name will be generated
     ** @return this
     */
    @Override
    public Printed withName(final String processorName) {
        this.processorName = processorName;
        return this;
    }
}