How to Autowire a Component which is having constr

问题:

I have a class having Autowired Constructor.

now when i am autowiring this class object in my class. how do i pass arguments for constructor??

example code: Class having Autowired Constructor:

@Component
public class Transformer {
    private String dataSource;
    @Autowired
    public Transformer(String dataSource)
    {
        this.dataSource = dataSource;
    }
}

Class using autowire for component having constructor with arguments:

@Component
    public class TransformerUser {
        private String dataSource;
        @Autowired
        public TransformerUser(String dataSource)
        {
            this.dataSource = dataSource;
        }
        @Autowired
        Transformer transformer;

    }

this code fails with message

"Unsatisfied dependency expressed through constructor parameter 0"

while creating bean of type Transformer.

how do i pass the arguments to Transformer while Autorwiring it??

回答1:

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;

import lombok.extern.slf4j.Slf4j;

@Slf4j
public class Transformer {
    private String datasource;

    @Autowired
    public Transformer(String datasource) {
        this.datasource=datasource;
        log.info(datasource);
    }
}

Then create a config file

package com.example.demo;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class BeanConfig {
    @Bean
    public Transformer getTransformerBean() {
        return new Transformer("hello spring");
    }

    @Bean
    public String getStringBean() {
        return new String();
    }
}

回答2:

you can use resource files

1) define a file like database.properties and put a variable like

datasource=example

in this file

2) define a configuration class

@Configuration
@PropertySource(value = {"classpath:resources/database.properties"})
public class PKEServiceFactoryMethod {

   private final Environment environment;

   @Bean
   public String dataSource() {
      return environment.getProperty("dataSource");
   }
}

also you can use placeholder that is much better of using constructor in this case

@Component
@PropertySource(value = {"classpath:resources/database.properties"})
public class Transformer {
    @Value("${dataSource}")
    private String dataSource;
}