Property or field 'config' cannot be found on null - spring

Question

I am trying to Implement InitializingBean on my StudentDaoImpl.class and in the function afterPropertiesSet() trying to execute an expression using ExpressionParser, but Spring is saying that property config is not found or is null even if I have declared config in my App.propperties.
AppConfig.class(Configuration Class)
package config;
import dao.StudentDAOImpl;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import javax.sql.DataSource;
#Configuration
#PropertySource("classpath:App.properties")
public class AppConfig {
#Bean("jdbcTemplete")
public JdbcTemplate jdbcTemplate() {
JdbcTemplate template = new JdbcTemplate();
template.setDataSource(dataSource());
return template;
}
#Bean("dataSource")
public DataSource dataSource() {
DriverManagerDataSource ds = new DriverManagerDataSource();
ds.setDriverClassName("com.mysql.cj.jdbc.Driver");
ds.setUrl("jdbc:mysql://localhost:3306/springjdbc");
ds.setUsername("root");
ds.setPassword("root");
return ds;
}
#Bean("StudentDaoImpl")
public StudentDAOImpl studentDaoImpl() {
StudentDAOImpl studentdao = new StudentDAOImpl(jdbcTemplate());
return studentdao;
}
#Bean("getProperties")
public static PropertySourcesPlaceholderConfigurer getProperties() {
return new PropertySourcesPlaceholderConfigurer();
}
}
StudentDaoImpl.class (I have removed methods of StudentDao Interface from the code below for you to see properly)
package dao;
import entities.Student;
import mapper.StudentMapper;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.RowMapper;
import java.util.List;
public class StudentDAOImpl implements StudentDAO, InitializingBean {
private JdbcTemplate jdbcTemplate;
#Value("${config}")
String s;
public StudentDAOImpl(JdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
#Override
public void afterPropertiesSet() throws Exception {
ExpressionParser expressionParser = new SpelExpressionParser();
System.out.println(s);
Expression expression = expressionParser.parseExpression("config");
String result = (String)expression.getValue();
System.out.println(result);
// if(result == true) {
// System.out.println("[Configuration]: Java Configuration");
// } else {
// System.out.println("[Configuration]: XML Configuration");
// }
}
}
App.properties
config=java
Also, I have seen that I was able to access the property from App.properties using #Value but not with ExpressionParser, Please help me solve this issue.

Answer 1

?
You are parsing a String, not the field; use
Expression expression = expressionParser.parseExpression(config);
to parse an expression in field config - however the value java is not a valid expression.
It is not at all clear what you are trying to do.