java - 如何在 Spring Boot 中配置外部配置 bean？

Question

我在尝试让多模块 spring boot 应用程序运行的最新迭代中遇到了问题，我设法将问题归结为粘贴在下面的一个简单的测试应用程序(也可以在这个要点上找到:https://gist.github.com/deinspanjer/d8416e91c1454bfe44efeee5b00fb805

当我尝试运行它时，它启动了，但随后出现以下错误。请告诉我我做错了什么明显的事情。 :(

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.4.2.RELEASE)

2016-12-10 16:41:04.035  INFO 25026 --- [           main] com.example.DemoApplication              : Starting DemoApplication on den with PID 25026 (/Users/dre/src/demo/target/classes started by dre in /Users/dre/src/demo)
2016-12-10 16:41:04.039  INFO 25026 --- [           main] com.example.DemoApplication              : No active profile set, falling back to default profiles: default
2016-12-10 16:41:04.108  INFO 25026 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@21507a04: startup date [Sat Dec 10 16:41:04 EST 2016]; root of context hierarchy
2016-12-10 16:41:04.923  WARN 25026 --- [           main] s.c.a.AnnotationConfigApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'demoApplication': Unsatisfied dependency expressed through field 'dc'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'demoConfig' defined in file [/Users/dre/src/demo/target/classes/com/example/config/DemoConfig.class]: Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'java.lang.String' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}
2016-12-10 16:41:04.932  INFO 25026 --- [           main] utoConfigurationReportLoggingInitializer : 

Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled.
2016-12-10 16:41:05.035 ERROR 25026 --- [           main] o.s.b.d.LoggingFailureAnalysisReporter   : 

***************************
APPLICATION FAILED TO START
***************************

Description:

Parameter 0 of constructor in com.example.config.DemoConfig required a bean of type 'java.lang.String' that could not be found.


Action:

Consider defining a bean of type 'java.lang.String' in your configuration.


Process finished with exit code 1

应用程序.yml

demo:
  foo:
    str_val: Make it work!
    objVal.objVal: This one too!

DemoApplication.java

package com.example;

import com.example.config.DemoConfig;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication implements ApplicationRunner {

    @Autowired
    private DemoConfig dc;

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.printf("String val: %s\nObject val: %s", dc.getStrVal(), dc.getObjVal());
    }
}

DemoConfig.java

package com.example.config;

import lombok.Data;
import org.hibernate.validator.constraints.NotBlank;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

@Data
@Component
@ConfigurationProperties(prefix = "demo.foo")
public class DemoConfig {
    @NotBlank private final String strVal;
    private final ObjVal objVal;

    @Data
    public static class ObjVal {
        @NotBlank private final String objVal;
    }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

Answer 1

阅读文档应该会有帮助。

您的字段是最终的，不会生成任何 setter 。然而，this is a requirement for @ConfigurationProperties properties .绑定(bind)确实通过标准 Java Beans 属性描述符工作。 Binder 从不支持构造函数注入(inject)。

但那个错误是不同的。依赖注入(inject)与这里的任何其他组件没有什么不同。您基本上是在创建一个 @Component，它接受一个 String 和一个 ObjVal 作为参数。因此，当应用程序上下文尝试创建 bean 时，它需要找到两个匹配这些类型的 bean。这与 @ConfigurationProperties 无关。

长话短说，按如下方式更改类:

package com.example.config;

import org.hibernate.validator.constraints.NotBlank;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

@Component
@ConfigurationProperties(prefix = "demo.foo")
public class DemoConfig {
    @NotBlank private String strVal;
    private final ObjVal objVal = new ObjVal();

   // getter & setter for strVal

   // getter for objVal (we already have an instance so we can "crawl to it")

    public static class ObjVal {
        @NotBlank private String objVal;

        // getter & setter for objVal
  }
}

我已经删除了 Lombok 以明确表示现在没有特定的构造函数。如果有，参数必须是上下文中可用的 spring bean。