Bean configuration override in boot

problem ：

      The project refers to a third party jar package , Need to be right @Configuration Configure one of the classes bean To cover . The service startup process encountered bean Registered exception 、 Newly added bean The problem of not loading .

  give an example ：

  The third party jar package MybatisPlusConfig class

@Configuration
public class MybatisPlusConfig {
    @Bean
    public MybatisPlusInterceptor innerInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        // Pagination 
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        // Optimism lock 
        interceptor.addInnerInterceptor(new OptimisticLockerInnerInterceptor());
        interceptor.addInnerInterceptor(new TenantLineInnerInterceptor(this.tenantLineHandler()));
        interceptor.addInnerInterceptor(new SystemLineInnerInterceptor(this.systemLineHandler()));
        return interceptor;
    }

}

The current project MybatisPrimaryConfig class

public class MybatisPrimaryConfig {

    @Bean
    public MybatisPlusInterceptor innerInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        // Pagination 
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        // Optimism lock 
        interceptor.addInnerInterceptor(new OptimisticLockerInnerInterceptor());
        interceptor.addInnerInterceptor(new SystemLineInnerInterceptor(this.systemLineHandler()));
        return interceptor;
    }

}

 1. The train of thought is MybatisPrimaryConfig Class method bean name innerInterceptor Cover MybatisPlusConfig Class method bean name innerInterceptor

 2. The step is to springboot in ,allowBeanDefinitionOverriding The default is false;spring The default is true. Need to be in application.properties Newly added spring.main.allow-bean-definition-overriding=true.

 3. bean Loading order
To configure allowBeanDefinitionOverriding by true after , But there is a problem that the new configuration is not registered [email protected] Properties of scanBasePackages Array , register bean when , It is registered in array order . Write the package name of the referenced package in front of the project package name , Only the configuration class in the project can override the reference package [email protected](scanBasePackages={"com.qm.qfc.common.entity.config","com.qm.qfc.dpf.dpfservice"})

1.spring Medium org.springframework.context.annotation.ComponentScanAnnotationParser Package scan code 

 public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {
        ....
        Set<String> basePackages = new LinkedHashSet();
        String[] basePackagesArray = componentScan.getStringArray("basePackages");
        String[] var19 = basePackagesArray;
        int var21 = basePackagesArray.length;

        int var22;
        for(var22 = 0; var22 < var21; ++var22) {
            String pkg = var19[var22];
            String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg), ",; \t\n");
            Collections.addAll(basePackages, tokenized);
        }

        Class[] var20 = componentScan.getClassArray("basePackageClasses");
        var21 = var20.length;

        for(var22 = 0; var22 < var21; ++var22) {
            Class<?> clazz = var20[var22];
            basePackages.add(ClassUtils.getPackageName(clazz));
        }

        if (basePackages.isEmpty()) {
            basePackages.add(ClassUtils.getPackageName(declaringClass));
        }

        scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
            protected boolean matchClassName(String className) {
                return declaringClass.equals(className);
            }
        });
        return scanner.doScan(StringUtils.toStringArray(basePackages));
    }

2. In the method 1 View in doScan The method is in org.springframework.context.annotation.ClassPathBeanDefinitionScanner class 

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
Assert.notEmpty(basePackages, "At least one base package must be specified");
Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
// In turn basePackages Class configured in 
for (String basePackage : basePackages) {
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
...
}
return beanDefinitions;
}