使用OpenCSV将Java bean映射到CSV

将JavaBean（对象）转换为CSV文件的需求非常普遍，将Bean写入CSV文件的方法有很多，但将JavaBean映射到CSV的最佳方法之一是使用OpenCSV库。在OpenCSV中有一个类名 StatefulBeanToCsvBuilder 这有助于将JavaBean转换为CSV。

1. 第一项任务是 将OpenCSV库添加到项目中 .
   • 对于maven项目，在pom中包含OpenCSV maven依赖项。xml文件。

     < dependency > < groupId >com.opencsv</ groupId > < artifactId >opencsv</ artifactId > < version >4.1</ version > </ dependency >

   • 对于Gradle项目，包括OpenCSV依赖项。

     compile group: 'com.opencsv', name: 'opencsv', version: '4.1'

   • 你可以下载 OpenCSV Jar 并包含在项目类路径中。
2. 将JavaBeans映射到CSV 下面是将JavaBean映射到CSV的分步过程。
   1. 创建Writer实例，将数据写入CSV文件。

      Writer writer = Files.newBufferedWriter(Paths.get(file_location));

   2. 创建需要写入CSV文件的对象列表。
   3. 使用ColumnPositionMapping策略将创建对象的列映射到csv的列。 这是一个可选步骤。如果未使用ColumnPositionMappingStrategy，则对象将以与对象的属性名相同的列名写入csv。

      ColumnPositionMappingStrategy mappingStrategy = new ColumnPositionMappingStrategy();
          mappingStrategy.setType(Employee.class);
      
      where Employee is the object to be mapped with CSV.
      

   4. 创建对象 州政府 创建StatefulBeanToCsvBuilder后，调用StatefulBeanToCsvBuilder类的生成方法，以writer对象为参数初始化。根据要求，用户还可以提供：
      • 列位置映射策略 借助于 使用映射策略 StatefulBeanToCsvBuilder对象的函数。
      • 借助于生成的csv文件的分隔符 带分离器 功能 StatefulBeanToCsvBuilder 对象
      • withQuotechar 在 withQuotechar 功能 StatefulBeanToCsvBuilder 对象

      StatefulBeanToCsv beanToCsv = new StatefulBeanToCsvBuilder(writer)
      .withMappingStrategy(mappingStrategy)
      . withSeparator('#')
                          .withQuotechar(CSVWriter.NO_QUOTE_CHARACTER)
                          .build();
      

   5. 创建StatefulBeanToCsv类的对象后，可以借助StatefulBeanToCsv对象的写入方法将对象或对象列表添加到csv文件中。

      beanToCsv.write(Employeelist);
      

例子： 在本例中，我们将创建Employee对象的列表，该列表具有名称、年龄、公司、薪水等属性。然后我们将生成一个CSV文件。包含员工对象的csv。 代码：

1. 受雇者JAVA

   public class Employee { public String Name, Age, Company, Salary; public Employee(String name, String age, String company, String salary) { super (); Name = name; Age = age; Company = company; Salary = salary; } @Override public String toString() { return "Employee [Name=" + Name + ", Age= " + Age + " , Company= " + Company + " , Salary= " + Salary + " ]"; } }

2. Beantosv。JAVA

   import java.io.FileWriter; import java.io.Writer; import java.nio.*; import java.nio.file.Files; import java.nio.file.Paths; import java.util.*; import com.opencsv.bean.ColumnPositionMappingStrategy; import com.opencsv.bean.StatefulBeanToCsv; import com.opencsv.bean.StatefulBeanToCsvBuilder; public class BeanToCSV { public static void main(String[] args) { // name of generated csv final String CSV_LOCATION = "Employees.csv " ; try { // Creating writer class to generate // csv file FileWriter writer = new FileWriter(CSV_LOCATION); // create a list of employee List<Employee> EmployeeList = new ArrayList<Employee>(); Employee emp1 = new Employee ( "Mahafuj" , "24" , "HTc" , "75000" ); Employee emp2 = new Employee ( "Aman" , "24" , "microsoft" , "79000" ); Employee emp3 = new Employee ( "Suvradip" , "26" , "tcs" , "39000" ); Employee emp4 = new Employee ( "Riya" , "22" , "NgGear" , "15000" ); Employee emp5 = new Employee ( "Prakash" , "29" , "Sath" , "51000" ); EmployeeList.add(emp1); EmployeeList.add(emp2); EmployeeList.add(emp3); EmployeeList.add(emp4); EmployeeList.add(emp5); // Create Mapping Strategy to arrange the // column name in order ColumnPositionMappingStrategy mappingStrategy= new ColumnPositionMappingStrategy(); mappingStrategy.setType(Employee. class ); // Arrange column name as provided in below array. String[] columns = new String[] { "Name" , "Age" , "Company" , "Salary" }; mappingStrategy.setColumnMapping(columns); // Creating StatefulBeanToCsv object StatefulBeanToCsvBuilder<Employee> builder= new StatefulBeanToCsvBuilder(writer); StatefulBeanToCsv beanWriter = builder.withMappingStrategy(mappingStrategy).build(); // Write list to StatefulBeanToCsv object beanWriter.write(EmployeeList); // closing the writer object writer.close(); } catch (Exception e) { e.printStackTrace(); } } }

输出 :

EmployeeData.csv
CSV file contains:-----

"Mahafuj", "24", "HTc", "75000"
"Aman", "24", "microsoft", "79000"
"Suvradip", "26", "tcs", "39000"
"Riya", "22", "NgGear", "15000"
"Prakash", "29", "Sath", "51000"

参考： BeanToCsv官方文件