简述

java读取csv的类库主要有两种，opencsv和javacsv，研究发现，javacsv在2014-12-10就不维护了。opencsv是apache的项目，并且至今仍在维护，所以项目中决定使用opencsv。

针对于maven 项目依赖 pom.xml 引入jar 如下：

<dependency><groupId>com.opencsv</groupId><artifactId>opencsv</artifactId><version>5.4</version>
</dependency>

 csv文件，全名 comma separated values，默认以逗号分隔，是纯文本文件。可以用记事本或者nodepad 打开看原始的文件内容。

例如：

name,age,birthday

jan,18,2002-09-09

macel,20,2001-08-09

读取方式：

• 逐行读取：

//read line by line
reader = new CSVReader(new FileReader("employees.csv"));
String[] nextLine;
while ((nextLine = reader.readNext()) != null) {System.out.println(nextLine[0] + "," + nextLine[1] + "," + nextLine[2] + "," + nextLine[3]);
}
reader.close();

• 全部读取：

CSVReader reader = new CSVReader(new FileReader("employees.csv"));
List<String[]> rows = reader.readAll();
for (String[] row : rows) {System.out.println(row[0] + "," + row[1] + "," + row[2] + "," + row[3]);
}

• 转换Java object ：

先写一个java类，例如：

public class Employee {public String firstName;public String lastName;public String email;public String department;//getters and setters@Overridepublic String toString() {return "Employee{" +"firstName='" + firstName + '\'' +", lastName='" + lastName + '\'' +", email='" + email + '\'' +", department='" + department + '\'' +'}';}
}

List<Employee> employees = new CsvToBeanBuilder(new FileReader("employees.csv")).withType(Employee.class).build().parse();
System.out.println(employees);

注解形式：

 @CsvBindByPosition  //该注解通过csv标题的位置打印数据

@CsvBindAndSplitByName(column = "Email"） //文件中标题的名字

@CsvNumber("###.##")  //针对于数值的验证输出

@CsvDate("yyyy-MM-dd") //日期格式的转换

等等

public class Employee {public String firstName;public String lastName;@CsvBindByName(column = "Email")public String contact;
...
...
}

写入方式 :

• 逐行写入

CSVWriter csvWriter = new CSVWriter(new FileWriter("list.csv"));
csvWriter.writeNext(new String[]{"John", "Doe", "jdoe@example.com", "Sales"});
csvWriter.writeNext(new String[]{"Jane", "Doe", "jane.doe@example.com", "HR"});
csvWriter.close();

• 全部写入：

List<String[]> lines = getRecordsAsList();
csvWriter = new CSVWriter(new FileWriter("list.csv"));
csvWriter.writeAll(lines);
csvWriter.close();

• 按sql查询写入：

csvWriter = new CSVWriter(new FileWriter("list.csv"));
Connection connection = DriverManager.getConnection("");
Statement stmt = connection.createStatement();
ResultSet resultSet = stmt.executeQuery("select * from employees");
csvWriter.writeAll(resultSet, true);
csvWriter.close();
connection.close();

• java 类写入：

List<Employee> employees = getListOfEmployeesFromSomewhere();
Writer writer = new FileWriter("employees.csv");
StatefulBeanToCsv beanToCsv = new StatefulBeanToCsvBuilder(writer).build();
beanToCsv.write(employees);
writer.close();

实战：

一行一行写入 + java类 

过滤器（CsvToBeanFilter）：opencsv提供了过滤器，可以过滤某些行，比如page header、page footer等

/*** 该 Filter 用于过滤到统计数据的部分，并单独存储在变量中以共后续的查询核对*/public class OrderReadToBeanFilter implements CsvToBeanFilter {/*** 文件中的总交易笔数/金额数据*/String[] billSummaryInfo;@Overridepublic boolean allowLine(String[] line) {
//最后一行的列长度为2 if (line.length > 2) {return true;} else if (line.length == 2) {billSummaryInfo = line;}return false;}}

读取文件中内容示例： 

部分代码块：	//获取文件流
InputStream ins = sftpUtils.getFile("文件路径");OrderReadToBeanFilter myFilter = new OrderReadToBeanFilter();//获取记录信息 转成实体类 OrderList<Order> OrderList = new CsvToBeanBuilder(new InputStreamReader(ins, StandardCharsets.UTF_8)).withSkipLines(1).withSeparator(',').withFilter(myFilter).withType(Order.class).build().parse();if (CollectionUtils.isEmpty(OrderList)) {String message = "信息为空！";moveFailFile(sftpUtils, channelNextDirDD, fileName, readingFilePath, message);return null;}//计算记录总和long amountSum = OrderList.stream().mapToLong(OrderList::getTransAmount).sum();//获取文件中汇总信息String[] billSummaryInfo = myFilter.billSummaryInfo;

写文件csv 示例：

//创建本地文件File file = new File("文件路径");if (!file.getParentFile().exists()) {//如果父目录不存在，创建父目录file.getParentFile().mkdirs();}file = new File(fullPath);file.createNewFile();log.info("file local path:{}", file.getAbsolutePath());//将数据写入csv文件CSVWriter csvWriter = new CSVWriter(new FileWriter(fullPath, StandardCharsets.UTF_8));// 先写标题csvWriter.writeNext("{"交易时间", "金额","流水号"}");//写入记录数据StatefulBeanToCsv beanToCsv = new StatefulBeanToCsvBuilder(csvWriter).build();beanToCsv.write(resultList);//写入汇总数据csvWriter.writeNext("{"总条数", "总额"}");//业务订单总额long sum = resultList.stream().mapToLong(Order::getTransAmount).sum();csvWriter.writeNext(new String[]{String.valueOf(resultList.size()), String.valueOf(sum)});csvWriter.close();

引用链接：OpenCSV for Reading and Writing CSV file in Java - SpringHowLet’s take a look at reading and writing CSV files in java using OpenCSV with a few examples. First of all, OpenCSV is a CSV file (comma-separated values)https://springhow.com/opencsv/