如何将HashMap写入CSV？
我有一个方法countOcc()打印一个列表（如下）。
1:00 ==> 1 hits(s) 2:00 ==> 4 hits(s) 3:00 ==> 3 hits(s) 4:00 ==> 6 hits(s) 5:00 ==> 14 hits(s) 6:00 ==> 26 hits(s) 7:00 ==> 16 hits(s) 8:00 ==> 25 hits(s) 9:00 ==> 34 hits(s) 10:00 ==> 39 hits(s) 11:00 ==> 33 hits(s) 12:00 ==> 50 hits(s) 13:00 ==> 49 hits(s) 14:00 ==> 51 hits(s) 15:00 ==> 53 hits(s) 16:00 ==> 40 hits(s) 17:00 ==> 20 hits(s) 18:00 ==> 33 hits(s) 19:00 ==> 26 hits(s) 20:00 ==> 18 hits(s) 21:00 ==> 29 hits(s) 22:00 ==> 7 hits(s)
方法：
public void countOcc(ArrayList list) { String aout = new String(); System.out.println("\n"); Integer[] numbers = list.toArray(new Integer[list.size()]); Map map = new HashMap(); for (int i = 0; i " + occurrence + " hits(s)"); } }
我想在其输出上有一个csv文件：
1:00,2:00,3:00,4:00,5:00,6:00,7:00,8:00,9:00,10:00,11:00,12:00 1,4,3,6,14,26,16,25,34,39,33,50
我知道opencsv，但我真的不知道如何在HashMap中使用它。
你有没有看过SuperCSV？ 该框架内置了CsvMapWriter： http ：//super-csv.github.io/super-csv/examples_writing.html
您基本上将标题定义为数组（您可以使用映射的排序键集），然后使用以下命令编写映射：
mapWriter.write(map, header, processors);
关闭这个opencsv教程 ：
Map values = new HashMap<>(); for (String line : lines) { String[] parts = line.split(" "); String time = parts[0]; String value = parts[2]; values.put(time, value); } StringWriter writer_ = new StringWriter(); CSVWriter writer = new CSVWriter(writer_); writer.writeNext(values.keySet().toArray()); writer.writeNext(values.values().toArray()); writer.close(); System.out.println(writer_.toString());
这给出了你的输出。
这是写入CSV文件的示例，您可以相应地自定义它：
import java.io.FileWriter; import java.io.IOException; import java.util.ArrayList; import java.util.List; public class CsvFileWriter { //Delimiter used in CSV file private static final String COMMA_DELIMITER = ","; private static final String NEW_LINE_SEPARATOR = "\n"; //CSV file header private static final String FILE_HEADER = "id,firstName,lastName,gender,age"; public static void writeCsvFile(String fileName) { //Create new students objects Student student1 = new Student(1, "Ahmed", "Mohamed", "M", 25); Student student2 = new Student(2, "Sara", "Said", "F", 23); Student student3 = new Student(3, "Ali", "Hassan", "M", 24); Student student4 = new Student(4, "Sama", "Karim", "F", 20); Student student5 = new Student(5, "Khaled", "Mohamed", "M", 22); Student student6 = new Student(6, "Ghada", "Sarhan", "F", 21); //Create a new list of student objects List students = new ArrayList(); students.add(student1); students.add(student2); students.add(student3); students.add(student4); students.add(student5); students.add(student6); FileWriter fileWriter = null; try { fileWriter = new FileWriter(fileName); //Write the CSV file header fileWriter.append(FILE_HEADER.toString()); //Add a new line separator after the header fileWriter.append(NEW_LINE_SEPARATOR); //Write a new student object list to the CSV file for (Student student : students) { fileWriter.append(String.valueOf(student.getId())); fileWriter.append(COMMA_DELIMITER); fileWriter.append(student.getFirstName()); fileWriter.append(COMMA_DELIMITER); fileWriter.append(student.getLastName()); fileWriter.append(COMMA_DELIMITER); fileWriter.append(student.getGender()); fileWriter.append(COMMA_DELIMITER); fileWriter.append(String.valueOf(student.getAge())); fileWriter.append(NEW_LINE_SEPARATOR); } System.out.println("CSV file was created successfully !!!"); } catch (Exception e) { System.out.println("Error in CsvFileWriter !!!"); e.printStackTrace(); } finally { try { fileWriter.flush(); fileWriter.close(); } catch (IOException e) { System.out.println("Error while flushing/closing fileWriter !!!"); e.printStackTrace(); } } } }
正如本文所解释的那样 ，写入CSV文件就像写入文本文件一样。
public static void write() { StringBuilder out = new StringBuilder(); for (int key : map.keySet()) { out.append(key + ":00,"); } // remove last ',' from line out = new StringBuilder(out.substring(0, out.length() - 1)); for (int occurence : map.values()) { out.append(occurence + ","); } // remove last ',' from line out = new StringBuilder(out.substring(0, out.length() - 1)); try (FileWriter fw = new FileWriter("my.csv")) { writer.append(out.toString()); } catch (IOException e) { e.printStackTrace(); } }
你可能需要这个：
public static void countOcc(List list) { Map map = new HashMap<>(); for (Integer key : list) { if (map.containsKey(key)) { map.put(key, map.get(key) + 1); } else { map.put(key, 1); } } String csv = "d://data.csv"; try (CSVWriter writer = new CSVWriter(new FileWriter(csv))) { String[] keysArray = new String[map.keySet().size()]; String[] valuesArray = new String[map.values().size()]; int counter = 0; for (Entry entry : map.entrySet()) { keysArray[counter] = entry.getKey() + ":00"; valuesArray[counter] = entry.getValue() + ""; counter++; } writer.writeNext(keysArray); writer.writeNext(valuesArray); } catch (IOException e) { e.printStackTrace(); } }