Java tutorial
/* * #%L * csv-scripts * %% * Copyright (C) 2014 Anton Hrytsenko * %% * 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. * #L% */ package hrytsenko.csv; import static java.nio.charset.StandardCharsets.UTF_8; import static java.nio.file.Files.newBufferedWriter; import static java.nio.file.Files.newInputStream; import groovy.lang.Closure; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.Reader; import java.io.Writer; import java.nio.charset.Charset; import java.nio.file.Path; import java.nio.file.Paths; import java.nio.file.StandardOpenOption; import java.util.ArrayList; import java.util.Collection; import java.util.Iterator; import java.util.LinkedHashSet; import java.util.List; import java.util.Map; import java.util.Set; import org.apache.commons.io.input.BOMInputStream; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import com.fasterxml.jackson.databind.ObjectReader; import com.fasterxml.jackson.databind.ObjectWriter; import com.fasterxml.jackson.dataformat.csv.CsvMapper; import com.fasterxml.jackson.dataformat.csv.CsvSchema; /** * Methods for input/output. * * <p> * Supported named arguments: * <dl> * <dt>path</dt> * <dd>Path to file.</dd> * <dt>records</dt> * <dd>The list of records to be saved.</dd> * <dt>charset</dt> * <dd>Charset for file, see standard charsets in {@link Charset}, default: UTF-8.</dd> * <dt>separator</dt> * <dd>Separator for values of fields, default: comma (',').</dd> * <dt>qualifier</dt> * <dd>Qualifier for values of fields, default: double-quote ('"').</dd> * </dl> * * @author hrytsenko.anton */ public final class IO { private static final Logger LOGGER = LoggerFactory.getLogger("APP"); private IO() { } /** * Gets records from file. * * @param args * the named arguments {@link IO}. * * @return the loaded records. * * @throws IOException * if file could not be read. */ public static List<Record> load(Map<String, ?> args) throws IOException { return load(args, null); } /** * Gets records from file. * * <p> * If closure is given, then it will be applied to each record. * * @param args * the named arguments {@link IO}. * @param closure * the closure to be applied to each record. * * @return the loaded records. * * @throws IOException * if file could not be read. */ public static List<Record> load(Map<String, ?> args, Closure<?> closure) throws IOException { Path path = getPath(args); LOGGER.info("Load: {}.", path.getFileName()); try (InputStream dataStream = newInputStream(path, StandardOpenOption.READ); InputStream bomStream = new BOMInputStream(dataStream); Reader dataReader = new InputStreamReader(bomStream, getCharset(args))) { CsvSchema csvSchema = getSchema(args).setUseHeader(true).build(); CsvMapper csvMapper = new CsvMapper(); ObjectReader csvReader = csvMapper.reader(Map.class).with(csvSchema); Iterator<Map<String, String>> rows = csvReader.readValues(dataReader); List<Record> records = new ArrayList<>(); while (rows.hasNext()) { Map<String, String> row = rows.next(); Record record = new Record(); record.putAll(row); records.add(record); if (closure != null) { closure.call(record); } } return records; } } /** * Saves records into CSV file. * * <p> * If file already exists, then it will be overridden. * * @param args * the named arguments {@link IO}. * * @throws IOException * if file could not be written. */ public static void save(Map<String, ?> args) throws IOException { Path path = getPath(args); LOGGER.info("Save: {}.", path.getFileName()); @SuppressWarnings("unchecked") Collection<Record> records = (Collection<Record>) args.get("records"); if (records.isEmpty()) { LOGGER.info("No records to save."); return; } try (Writer dataWriter = newBufferedWriter(path, getCharset(args), StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING)) { Set<String> columns = new LinkedHashSet<>(); List<Map<String, String>> rows = new ArrayList<>(); for (Record record : records) { Map<String, String> values = record.values(); columns.addAll(values.keySet()); rows.add(values); } CsvSchema.Builder csvSchema = getSchema(args).setUseHeader(true); for (String column : columns) { csvSchema.addColumn(column); } CsvMapper csvMapper = new CsvMapper(); ObjectWriter csvWriter = csvMapper.writer().withSchema(csvSchema.build()); csvWriter.writeValue(dataWriter, rows); } } static Path getPath(Map<String, ?> args) { CharSequence path = (CharSequence) args.get("path"); if (path == null) { throw new IllegalArgumentException("Path not defined."); } return Paths.get(path.toString()); } static Charset getCharset(Map<String, ?> args) { CharSequence charsetName = (CharSequence) args.get("charset"); return charsetName != null ? Charset.forName(charsetName.toString()) : UTF_8; } static CsvSchema.Builder getSchema(Map<String, ?> args) { CharSequence separator = (CharSequence) args.get("separator"); if (separator == null) { separator = ","; } if (separator.length() != 1) { throw new IllegalArgumentException("Use single character as separator."); } CharSequence qualifier = (CharSequence) args.get("qualifier"); if (qualifier == null) { qualifier = "\""; } if (qualifier.length() != 1) { throw new IllegalArgumentException("Use single character as qualifier."); } CsvSchema.Builder schema = CsvSchema.builder(); schema.setColumnSeparator(separator.charAt(0)); schema.setQuoteChar(qualifier.charAt(0)); return schema; } }