将数据从数据库写入.csv文件
您可以使用OpenCSV库将数据写入.csv文件，还可以使用mysql-java-connector通过Java程序与MySQL数据库进行通信。
Maven依赖
以下是需要包含在pom.xml文件中以从数据库表将数据写入.csv文件的依赖项。
<dependency> <groupId>com.opencsv</groupId> <artifactId>opencsv</artifactId> <version>4.4</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-lang3</artifactId> <version>3.9</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.6</version> </dependency>
将数据写入CSV文件
com.opencsv软件包的CSVWriter类表示一个简单的CSV编写器。在实例化此类时，您需要传递一个Writer对象作为其构造函数的参数，该对象代表您要向其写入数据的文件。它提供名为writeAll()和writeNext()的方法以将数据写入.csv文件
使用writeNext()方法
writeNext()CSVWriter类的方法将下一行写入.csv文件
示例
假设我们已经创建了一个名为empDetails的表，并使用以下查询填充了该表-
CREATE TABLE empDetails (ID INT, Name VARCHAR(255), Salary INT, start_date VARCHAR(255), Dept VARCHAR(255)); Insert INTO empDetails values (1, 'Krishna', 2548, '2012-01-01', 'IT'); Insert INTO empDetails values (2, 'Vishnu', 4522, '2013-02-26', 'Operations'); Insert INTO empDetails values (3, 'Raja', 3021, '2016-10-10', 'HR'); Insert INTO empDetails values (4, 'Raghav', 6988, '2012-01-01', 'IT');
以下Java程序从上面创建的表中创建一个csv文件。
import java.io.FileWriter;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import com.opencsv.CSVWriter;
public class DbToCSV {
public static void main(String args[]) throws SQLException, IOException {
//获得连接
String url = "jdbc:mysql://localhost/mydb";
Connection con = DriverManager.getConnection(url, "root", "password");
System.out.println("Connection established......");
//创建语句
Statement stmt = con.createStatement();
//查询以检索记录
String query = "Select * from empDetails";
//执行查询
stmt.executeQuery("use mydb");
ResultSet rs = stmt.executeQuery(query);
//实例化CSVWriter类
CSVWriter writer = new CSVWriter(new FileWriter("D://output.csv"));
ResultSetMetaData Mdata = rs.getMetaData();
Mdata.getColumnName(1);
//将数据写入CSV文件
String line1[] = {Mdata.getColumnName(1), Mdata.getColumnName(2), Mdata.getColumnName(3), Mdata.getColumnName(4), Mdata.getColumnName(5)};
writer.writeNext(line1);
String data[] = new String[5];
while(rs.next()) {
data[0] = new Integer(rs.getInt("ID")).toString();
data[1] = rs.getString("Name");
data[2] = new Integer(rs.getInt("Salary")).toString();
data[3] = rs.getString("start_date");
data[4] = rs.getString("Dept");
writer.writeNext(data);
}
//将数据从写入器刷新到文件
writer.flush();
System.out.println("Data entered");
}
}输出结果
Connection established...... Data entered
如果您验证生成的.csv文件，则可以观察其内容，如下所示：
"ID","Name","Salary","start_date","Dept" "1","Krishna","2548","2012-01-01","IT" "2","Vishnu","4522","2013-02-26","Operations" "3","Raja","3021","2016-10-10","HR" "4","Raghav","6988","2012-01-01","IT"