[Java知识库]Boot 中bean配置覆盖

问题：

????? 项目引用第三方jar包，需要对@Configuration配置类中的某个bean进行覆盖。服务启动过程遇到了bean已被注册异常、新加的bean不加载的问题。

?举例：

?第三方jar包MybatisPlusConfig 类

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

}

当前项目MybatisPrimaryConfig 类

public class MybatisPrimaryConfig {

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

}

?1.思路是MybatisPrimaryConfig类的方法bean名字innerInterceptor覆盖MybatisPlusConfig类的方法bean名字innerInterceptor

?2.步骤是在springboot中，allowBeanDefinitionOverriding 默认为false；spring默认为true。需要在application.properties中新增spring.main.allow-bean-definition-overriding=true。

?3. bean加载顺序
配置allowBeanDefinitionOverriding为true后，却出现新配置不注册的问题。@SpringBootApplication的属性scanBasePackages数组，注册bean时，是按数组顺序注册的。把引用包的包名写在项目包名前面，项目中的配置类才可覆盖掉引用包的bean。@SpringBootApplication(scanBasePackages={"com.qm.qfc.common.entity.config","com.qm.qfc.dpf.dpfservice"})

1.spring中的org.springframework.context.annotation.ComponentScanAnnotationParser包扫描代码

 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.在方法1中查看doScan方法是在org.springframework.context.annotation.ClassPathBeanDefinitionScanner类

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
Assert.notEmpty(basePackages, "At least one base package must be specified");
Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
//依次对basePackages中配置的类进行注入
for (String basePackage : basePackages) {
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
...
}
return beanDefinitions;
}