使用 OpenCSV 将 Java Beans 映射到 CSV
原文:https://www . geesforgeks . org/mapping-Java-beans-to-CSV-using-opencsv/
将 java bean(Objects)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，但是将 Java Bean 映射到 CSV 的最佳方法之一是使用 OpenCSV 库。在 OpenCSV 中有一个类名stateflebeantosvbuilder，它有助于将 Java Beans 转换为 CSV。
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第一个任务是将 OpenCSV 库添加到项目中。
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对于 maven 项目，在 pom.xml 文件中包含 OpenCSV maven 依赖项。
java <dependency> <groupId>com.opencsv</groupId> <artifactId>opencsv</artifactId> <version>4.1</version> </dependency> -
对于 Gradle 项目，包括 OpenCSV 依赖项。
java compile group: 'com.opencsv', name: 'opencsv', version: '4.1' -
你可以下载 OpenCSV Jar 并包含在你的项目类路径中。
- 将 Java Beans 映射到 CSV 下面是将 Java Beans 映射到 CSV 的分步过程。
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创建用于将数据写入 CSV 文件的编写器实例。
java Writer writer = Files.newBufferedWriter(Paths.get(file_location)); -
创建需要写入 CSV 文件的对象列表。
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使用列位置映射策略将已创建对象的列映射到 csv 的列。 这是可选步骤。如果未使用 ColumnPositionMappingStrategy，则对象将被写入 csv，列名与对象的属性名相同。
```java ColumnPositionMappingStrategy mappingStrategy = new ColumnPositionMappingStrategy(); mappingStrategy.setType(Employee.class);
where Employee is the object to be mapped with CSV.
```
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创建 stateflebeantosvbuilder 后，通过调用 stateflebeantosvbuilder 类的 build 方法，以 writer 对象为参数，创建stateflebeantosv类的对象。根据需要用户也可以提供:
```java StatefulBeanToCsv beanToCsv = new StatefulBeanToCsvBuilder(writer) .withMappingStrategy(mappingStrategy) . withSeparator('#') .withQuotechar(CSVWriter.NO_QUOTE_CHARACTER) .build();
```
- column positionmapping strategy借助 withMappingStrategy 函数的 StatefulBeanToCsvBuilder 对象。
- 借助stateflebeantosvbuilder对象的分离函数对生成的 csv 文件进行分离。
- 借助stateflebeantosvbuilder对象的 withQuotechar 功能，生成 csv 文件的 withQuotechar 。
- 创建 stateflebeantosv 类的对象后，可以借助 stateflebeantosv 对象的 write 方法将对象或对象列表添加到 Csv 文件中。
```java beanToCsv.write(Employeelist);
```
示例:在本例中，我们将创建员工对象列表，该列表具有姓名、年龄、公司、工资等属性。然后我们将生成一个包含雇员对象的 CSV 文件 Employees.csv。 代码:
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Employee.javaT3
```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 + "]"; } } ```
T4】 2. BeanToCSV.javaT3
```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 EmployeeList = new ArrayList(); 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 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(); } } } ```
T4】
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:T2】beantosv 官方文档
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