JAVA语言之Spring源码解读之核心容器下节-职坐标

JAVA语言之Spring源码解读之核心容器下节

小标 2019-03-27 来源：阅读 671 评论 0

摘要：本文主要向大家介JAVA语言之Spring源码解读之核心容器下节绍了，通过具体的内容向大家展示，希望对大家学习JAVA语言有所帮助。

本文主要向大家介JAVA语言之Spring源码解读之核心容器下节绍了，通过具体的内容向大家展示，希望对大家学习JAVA语言有所帮助。

JAVA语言之Spring源码解读之核心容器下节

上一篇我们通过ClassPathXmlApplicationContext加载xml文件，通过BeanFactory获取实例bean的demo代码去解读了Spring Core Container中的spring-beans,spring-core,spring-context三个组件之间的一些具体类的实现。从加载XML、构造BeanFactory、到初始化Bean,已经有了一个全貌的了解。今天继续前一节，我们来说一下注解方式是如何实现bean是如何实现自动化装配和依赖加载的。

注解demo

package com.ckmike.dao.impl;

import com.ckmike.beans.Employee;
import com.ckmike.dao.EmployeeMapper;
import org.springframework.stereotype.Repository;

/**
 * EmployeeDao 简要描述
 * <p> TODO:描述该类职责 </p>
 *
 * @author ckmike
 * @version 1.0
 * @date 18-12-15 下午12:27
 * @copyright ckmike
 **/
@Repository(value = "employeeDao")
public class EmployeeDao implements EmployeeMapper {
    public Employee getEmployeeById() {
        return new Employee();
    }
}

package com.ckmike.service.impl;

import com.ckmike.beans.Employee;
import com.ckmike.dao.EmployeeMapper;
import com.ckmike.service.EmployeeService;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;

/**
 * EmployeeServiceImpl 简要描述
 * <p> TODO:描述该类职责 </p>
 *
 * @author ckmike
 * @version 1.0
 * @date 18-12-15 上午10:38
 * @copyright ckmike
 **/
@Service(value = "employeeService")
public class EmployeeServiceImpl implements EmployeeService {

    @Resource(name = "employeeDao")
    private EmployeeMapper employeeMapper;

    public Employee getEmployee() {
        return employeeMapper.getEmployeeById();
    }
}

import com.ckmike.beans.Employee;
import com.ckmike.config.SpringConfig;
import com.ckmike.service.EmployeeService;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4Cla***unner;

import javax.annotation.Resource;

/**
 * SpringCoreAnnotationTest 简要描述
 * <p> TODO:描述该类职责 </p>
 *
 * @author ckmike
 * @version 1.0
 * @date 18-12-15 下午12:19
 * @copyright ckmike
 **/
@RunWith(value = SpringJUnit4Cla***unner.class)
@ContextConfiguration(classes={SpringConfig.class})
public class SpringCoreAnnotationTest {

    @Resource(name="employeeService")
    private EmployeeService employeeService;

    @Test
    public void annotationTest() {
        Employee employee = employeeService.getEmployee();
        System.out.println(employee.toString());
    }

}

pom.xml文件

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

    <groupId>Spring-Core-Demo</groupId>
    <artifactId>com.ckmike.springcore.demo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- Spring的核心模块 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>5.1.3.RELEASE</version>
        </dependency>
        <!-- Beans模块 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>5.1.3.RELEASE</version>
        </dependency>
        <!-- 生命周期管理 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.1.3.RELEASE</version>
        </dependency>
        <!-- SPel模块 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-expression</artifactId>
            <version>5.1.3.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>5.1.2.RELEASE</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

这种方式是实际开发测试的流程，一般我们在Spring项目中会使用注解进行bean注册，这种方式和XML方式有什么不同呢？那种方式比较好呢？
注解方式：方便开发和使用，只要通过注解自动注入对象，解放了开发使用者。但是对于维护而言，各个注解是散落在各个类上的，如果你需要知道整个项目中bean的全貌，那么你需要频繁的切换到各个类。
XML管理方式：把所有的bean管理聚集在一起，维护查找起来非常方便。但是对于开发和使用者需要一起维护这个XML文件，对于开发使用者不太友好。
综合考虑：一般我们开发一个项目都会约定一些规则与共识，所以这两种方式都有存在的意义，具体选择结合项目人员、项目场景做出考量即可。

自动装配

从上面的注解方式自动装配方式，我们看@ContextConfiguration(classes={SpringConfig.class})，它依然是通过初始化Context来初始化Bean容器，只是这个时候我们不是从xml初始容器，而是通过扫描注解的方式自动注册bean到容器中。我们看下SpringConfig这个类做了什么：

/**
 * SpringConfig 简要描述
 * <p> TODO:描述该类职责 </p>
 *
 * @author ckmike
 * @version 1.0
 * @date 18-12-15 下午12:34
 * @copyright ckmike
 **/
@Configuration
@ComponentScan(basePackages={"com.ckmike"})
public class SpringConfig {

}

@ComponentScan指定扫描的根路径，扫描该路径下所有的注解，自动注册到Bean容器当中。我们继续看下@ComponentScan：

/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      //www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.beans.factory.support.BeanNameGenerator;
import org.springframework.core.annotation.AliasFor;
import org.springframework.core.type.filter.TypeFilter;

/**
 * Configures component scanning directives for use with @{@link Configuration} classes.
 * Provides support parallel with Spring XML's {@code <context:component-scan>} element.
 *
 * <p>Either {@link #basePackageClasses} or {@link #basePackages} (or its alias
 * {@link #value}) may be specified to define specific packages to scan. If specific
 * packages are not defined, scanning will occur from the package of the
 * class that declares this annotation.
 *
 * <p>Note that the {@code <context:component-scan>} element has an
 * {@code annotation-config} attribute; however, this annotation does not. This is because
 * in almost all cases when using {@code @ComponentScan}, default annotation config
 * processing (e.g. processing {@code @Autowired} and friends) is assumed. Furthermore,
 * when using {@link AnnotationConfigApplicationContext}, annotation config processors are
 * always registered, meaning that any attempt to disable them at the
 * {@code @ComponentScan} level would be ignored.
 *
 * <p>See {@link Configuration @Configuration}'s Javadoc for usage examples.
 *
 * @author Chris Beams
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since 3.1
 * @see Configuration
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Repeatable(ComponentScans.class)
public @interface ComponentScan {

    /**
     * Alias for {@link #basePackages}.
     * <p>Allows for more concise annotation declarations if no other attributes
     * are needed &mdash; for example, {@code @ComponentScan("org.my.pkg")}
     * instead of {@code @ComponentScan(basePackages = "org.my.pkg")}.
     */
    @AliasFor("basePackages")
    String[] value() default {};

    /**
     * Base packages to scan for annotated components.
     * <p>{@link #value} is an alias for (and mutually exclusive with) this
     * attribute.
     * <p>Use {@link #basePackageClasses} for a type-safe alternative to
     * String-based package names.
     */
    @AliasFor("value")
    String[] basePackages() default {};

    /**
     * Type-safe alternative to {@link #basePackages} for specifying the packages
     * to scan for annotated components. The package of each class specified will be scanned.
     * <p>Consider creating a special no-op marker class or interface in each package
     * that serves no purpose other than being referenced by this attribute.
     */
    Class<?>[] basePackageClasses() default {};

    /**
     * The {@link BeanNameGenerator} class to be used for naming detected components
     * within the Spring container.
     * <p>The default value of the {@link BeanNameGenerator} interface itself indicates
     * that the scanner used to process this {@code @ComponentScan} annotation should
     * use its inherited bean name generator, e.g. the default
     * {@link AnnotationBeanNameGenerator} or any custom instance supplied to the
     * application context at bootstrap time.
     * @see AnnotationConfigApplicationContext#setBeanNameGenerator(BeanNameGenerator)
     */
    Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;

    /**
     * The {@link ScopeMetadataResolver} to be used for resolving the scope of detected components.
     */
    Class<? extends ScopeMetadataResolver> scopeResolver() default AnnotationScopeMetadataResolver.class;

    /**
     * Indicates whether proxies should be generated for detected components, which may be
     * necessary when using scopes in a proxy-style fashion.
     * <p>The default is defer to the default behavior of the component scanner used to
     * execute the actual scan.
     * <p>Note that setting this attribute overrides any value set for {@link #scopeResolver}.
     * @see ClassPathBeanDefinitionScanner#setScopedProxyMode(ScopedProxyMode)
     */
    ScopedProxyMode scopedProxy() default ScopedProxyMode.DEFAULT;

    /**
     * Controls the class files eligible for component detection.
     * <p>Consider use of {@link #includeFilters} and {@link #excludeFilters}
     * for a more flexible approach.
     */
    String resourcePattern() default ClassPathScanningCandidateComponentProvider.DEFAULT_RESOURCE_PATTERN;

    /**
     * Indicates whether automatic detection of classes annotated with {@code @Component}
     * {@code @Repository}, {@code @Service}, or {@code @Controller} should be enabled.
     */
    boolean useDefaultFilters() default true;

    /**
     * Specifies which types are eligible for component scanning.
     * <p>Further narrows the set of candidate components from everything in {@link #basePackages}
     * to everything in the base packages that matches the given filter or filters.
     * <p>Note that these filters will be applied in addition to the default filters, if specified.
     * Any type under the specified base packages which matches a given filter will be included,
     * even if it does not match the default filters (i.e. is not annotated with {@code @Component}).
     * @see #resourcePattern()
     * @see #useDefaultFilters()
     */
    Filter[] includeFilters() default {};

    /**
     * Specifies which types are not eligible for component scanning.
     * @see #resourcePattern
     */
    Filter[] excludeFilters() default {};

    /**
     * Specify whether scanned beans should be registered for lazy initialization.
     * <p>Default is {@code false}; switch this to {@code true} when desired.
     * @since 4.1
     */
    boolean lazyInit() default false;

    /**
     * Declares the type filter to be used as an {@linkplain ComponentScan#includeFilters
     * include filter} or {@linkplain ComponentScan#excludeFilters exclude filter}.
     */
    @Retention(RetentionPolicy.RUNTIME)
    @Target({})
    @interface Filter {

        /**
         * The type of filter to use.
         * <p>Default is {@link FilterType#ANNOTATION}.
         * @see #classes
         * @see #pattern
         */
        FilterType type() default FilterType.ANNOTATION;

        /**
         * Alias for {@link #classes}.
         * @see #classes
         */
        @AliasFor("classes")
        Class<?>[] value() default {};

        /**
         * The class or classes to use as the filter.
         * <p>The following table explains how the classes will be interpreted
         * based on the configured value of the {@link #type} attribute.
         * <table border="1">
         * <tr><th>{@code FilterType}</th><th>Class Interpreted As</th></tr>
         * <tr><td>{@link FilterType#ANNOTATION ANNOTATION}</td>
         * <td>the annotation itself</td></tr>
         * <tr><td>{@link FilterType#ASSIGNABLE_TYPE ASSIGNABLE_TYPE}</td>
         * <td>the type that detected components should be assignable to</td></tr>
         * <tr><td>{@link FilterType#CUSTOM CUSTOM}</td>
         * <td>an implementation of {@link TypeFilter}</td></tr>
         * </table>
         * <p>When multiple classes are specified, <em>OR</em> logic is applied
         * &mdash; for example, "include types annotated with {@code @Foo} OR {@code @Bar}".
         * <p>Custom {@link TypeFilter TypeFilters} may optionally implement any of the
         * following {@link org.springframework.beans.factory.Aware Aware} interfaces, and
         * their respective methods will be called prior to {@link TypeFilter#match match}:
         * <ul>
         * <li>{@link org.springframework.context.EnvironmentAware EnvironmentAware}</li>
         * <li>{@link org.springframework.beans.factory.BeanFactoryAware BeanFactoryAware}
         * <li>{@link org.springframework.beans.factory.BeanClassLoaderAware BeanClassLoaderAware}
         * <li>{@link org.springframework.context.ResourceLoaderAware ResourceLoaderAware}
         * </ul>
         * <p>Specifying zero classes is permitted but will have no effect on component
         * scanning.
         * @since 4.2
         * @see #value
         * @see #type
         */
        @AliasFor("value")
        Class<?>[] classes() default {};

        /**
         * The pattern (or patterns) to use for the filter, as an alternative
         * to specifying a Class {@link #value}.
         * <p>If {@link #type} is set to {@link FilterType#ASPECTJ ASPECTJ},
         * this is an AspectJ type pattern expression. If {@link #type} is
         * set to {@link FilterType#REGEX REGEX}, this is a regex pattern
         * for the fully-qualified class names to match.
         * @see #type
         * @see #classes
         */
        String[] pattern() default {};

    }

}

如果不指定路径，那么就从classpath下面去扫描，lazyInit默认false，默认是通过BeanNameGenerator去生成bean，然后放入到容器中，其中还有scopedProxy，我们先来看看BeanNameGenerator接口的实现类：

/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      //www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.annotation;

import java.beans.Introspector;
import java.util.Map;
import java.util.Set;

import org.springframework.beans.factory.annotation.AnnotatedBeanDefinition;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanNameGenerator;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

/**
 * {@link org.springframework.beans.factory.support.BeanNameGenerator}
 * implementation for bean classes annotated with the
 * {@link org.springframework.stereotype.Component @Component} annotation
 * or with another annotation that is itself annotated with
 * {@link org.springframework.stereotype.Component @Component} as a
 * meta-annotation. For example, Spring's stereotype annotations (such as
 * {@link org.springframework.stereotype.Repository @Repository}) are
 * themselves annotated with
 * {@link org.springframework.stereotype.Component @Component}.
 *
 * <p>Also supports Java EE 6's {@link javax.annotation.ManagedBean} and
 * JSR-330's {@link javax.inject.Named} annotations, if available. Note that
 * Spring component annotations always override such standard annotations.
 *
 * <p>If the annotation's value doesn't indicate a bean name, an appropriate
 * name will be built based on the short name of the class (with the first
 * letter lower-cased). For example:
 *
 * <pre>com.xyz.FooServiceImpl -&gt; fooServiceImpl</pre>
 *
 * @author Juergen Hoeller
 * @author Mark Fisher
 * @since 2.5
 * @see org.springframework.stereotype.Component#value()
 * @see org.springframework.stereotype.Repository#value()
 * @see org.springframew