曹工说Spring Boot源码（4）-- 我是怎么自定义ApplicationContext，从json文件读取bean definition的？

写在前面的话

相关背景及资源：

曹工说Spring Boot源码系列开讲了（1）-- Bean Definition到底是什么，附spring思维导图分享

工程代码地址 思维导图地址

工程结构图：

大体思路

总体来说，bean definition是什么，我们前面几讲，说了个大概了；目前，我们将聚焦于怎么获取bean definition。

我们这次做个实验，就是将bean definition（一共两个bean，有依赖关系，依赖是手动指定的）定义在json文件内，然后自定义一个applicationcontext，从该文件内读取bean definiton，最后我们测试下是否能work。

注意哈，这里的依赖，依然和前面讲的一样，都是手动指定依赖，类似@Autowired这种，还会放到后面才会讲，开车也要先学手动档嘛，是伐？

建议大家直接拖源码下来看：

https://gitee.com/ckl111/spring-boot-first-version-learn/tree/master/all-demo-in-spring-learning/spring-beans-json-extend

定义json文件

json文件内，要表达bean definition，按照我们前面说的，基本就包括几个必要的就行了，比如beanClassName。但我这里还是展示一个完整的，但我也是用fastjson先在之前的工程里生成了一个json，之后再拷贝到了json文件里：

// 这里获取到的bean definition的实际类型是 GenericBeanDefiniton，所以序列化出来的的json，就是一个
// GenericBeanDefiniton集合的json
List<BeanDefinition> beanDefinitionList = factory.getBeanDefinitionList()
JSON.toJSONString(beanDefinitionList)

json文件内容如下：

[
  {
    "abstract": false,
    "autowireCandidate": true,
    "autowireMode": 0,
    "beanClass": "org.springframework.simple.TestService",
    "beanClassName": "org.springframework.simple.TestService",
    "constructorArgumentValues": {
      "argumentCount": 0,
      "empty": true,
      "genericArgumentValues": [],
      "indexedArgumentValues": {}
    },
    "dependencyCheck": 0,
    "enforceDestroyMethod": true,
    "enforceInitMethod": true,
    "lazyInit": false,
    "lenientConstructorResolution": true,
    "methodOverrides": {
      "empty": true,
      "overrides": []
    },
    "nonPublicAccessAllowed": true,
    "primary": false,
    "propertyValues": {
      "converted": false,
      "empty": true,
      "propertyValueList": [],
      "propertyValues": []
    },
    "prototype": false,
    "qualifiers": [],
    "resolvedAutowireMode": 0,
    "role": 0,
    "scope": "",
    "singleton": true,
    "synthetic": false
  },
  {
    "abstract": false,
    "autowireCandidate": true,
    "autowireMode": 0,
    "beanClass": "org.springframework.simple.byconstructor.TestControllerByConstructor",
    "beanClassName": "org.springframework.simple.byconstructor.TestControllerByConstructor",
    "constructorArgumentValues": {
      "argumentCount": 2,
      "empty": false,
      "genericArgumentValues": [],
      "indexedArgumentValues": {
        0: {
          "converted": false,
          "value": {
            "beanName": "testService",
            "toParent": false
          }
        },
        1: {
          "converted": false,
          "value": "wire by constructor"
        }
      }
    },
    "dependencyCheck": 0,
    "enforceDestroyMethod": true,
    "enforceInitMethod": true,
    "lazyInit": false,
    "lenientConstructorResolution": true,
    "methodOverrides": {
      "empty": true,
      "overrides": []
    },
    "nonPublicAccessAllowed": true,
    "primary": false,
    "propertyValues": {
      "converted": false,
      "empty": true,
      "propertyValueList": [],
      "propertyValues": []
    },
    "prototype": false,
    "qualifiers": [],
    "resolvedAutowireMode": 0,
    "role": 0,
    "scope": "",
    "singleton": true,
    "synthetic": false
  }
]

大家可能看得有点懵，其实换成xml，就是类似下面这样的：

	<bean name="testService" class="org.springframework.simple.TestService" />

	<bean id="testController" class="org.springframework.simple.TestController">
		<constructor-arg ref="testService"/>
	</bean>

扩展 applicationContext

package org.springframework.beans.extend.json.applicationcontext;

import org.springframework.beans.BeansException;
import org.springframework.beans.extend.json.JsonBeanDefinitionReader;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.xml.ResourceEntityResolver;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.AbstractRefreshableConfigApplicationContext;
import java.io.IOException;

public class ClassPathJsonApplicationContext extends AbstractRefreshableConfigApplicationContext {

    @Override
    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        //其实主要内容和xmlapplicationcontext是一样的，主要就是下面这行不一样，new了一个json reader
        JsonBeanDefinitionReader beanDefinitionReader = new JsonBeanDefinitionReader(beanFactory);

        beanDefinitionReader.setEnvironment(this.getEnvironment());
        beanDefinitionReader.setResourceLoader(this);
		// 这里通过json bean definiton reader去读取bean definition
        loadBeanDefinitions(beanDefinitionReader);
    }

	/**
	 *通过json bean definiton reader去读取bean definition
	 **/
    protected void loadBeanDefinitions(JsonBeanDefinitionReader reader) throws BeansException, IOException {
        // 这里获取json文件的path，这个location是在new ClassPathJsonApplicationContext时传进来的
        String[] configResources = getConfigLocations();
        if (configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }
    }

    public ClassPathJsonApplicationContext(String configLocation) throws BeansException {
        this(new String[] {configLocation}, true, null);
    }

	/**
	 * 这里一模一样，不需要任何变化
	 **/
    public ClassPathJsonApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
            throws BeansException {

        super(parent);
        setConfigLocations(configLocations);
        if (refresh) {
            refresh();
        }
    }
}

扩展jsonBeanDefinitionReader

package org.springframework.beans.extend.json;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.config.ConstructorArgumentValues;
import org.springframework.beans.factory.config.RuntimeBeanReference;
import org.springframework.beans.factory.support.AbstractBeanDefinitionReader;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanNameGenerator;
import org.springframework.beans.factory.support.GenericBeanDefinition;
import org.springframework.context.annotation.AnnotationBeanNameGenerator;
import org.springframework.core.NamedThreadLocal;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.EncodedResource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.util.CollectionUtils;
import org.springframework.util.StreamUtils;
import org.xml.sax.InputSource;

import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.Charset;
import java.util.*;

/**
 * 类似
 * {@link org.springframework.beans.factory.xml.XmlBeanDefinitionReader}
 * 只是本类是去json文件里读取bean definition
 *
 */
@Slf4j
public class JsonBeanDefinitionReader extends AbstractBeanDefinitionReader {
    private final ThreadLocal<Set<EncodedResource>> resourcesCurrentlyBeingLoaded =
            new NamedThreadLocal<Set<EncodedResource>>("json bean definition resources currently being loaded");

    public JsonBeanDefinitionReader(BeanDefinitionRegistry registry) {
        super(registry);
    }

    @Override
    public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
        // 以下照抄xmlbeanDefintionReader开始
        Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
        if (currentResources == null) {
            currentResources = new HashSet<EncodedResource>(4);
            this.resourcesCurrentlyBeingLoaded.set(currentResources);
        }

        EncodedResource encodedResource = new EncodedResource(resource);
        if (!currentResources.add(encodedResource)) {
            throw new BeanDefinitionStoreException(
                    "Detected cyclic loading of " + encodedResource + " - check your import definitions!");
        }
        //照抄xmlbeanDefintionReader结束

        //这里的encodedResource.getResource()就是我们的json文件，这里通过spring core里面的一个工具类读取为InputStream
        String json = null;
        try (InputStream inputStream = encodedResource.getResource().getInputStream()) {
            json = StreamUtils.copyToString(inputStream, Charset.forName("UTF-8"));
        } catch (IOException e) {
            log.error("{}",e);
            return 0;
        } finally {
            currentResources.remove(encodedResource);
            if (currentResources.isEmpty()) {
                this.resourcesCurrentlyBeingLoaded.remove();
            }
        }

        //熟悉的fastjson，熟悉的味道
        List<GenericBeanDefinition> list = JSON.parseArray(json, GenericBeanDefinition.class);
        if (CollectionUtils.isEmpty(list)) {
            return 0;
        }

        /**
         * 1：因为GenericBeanDefinition，只有setBeanClassName，所以bean反序列化时，只序列化了这个字		* 段；实际我们知道，beanClass很重要，所以我们只能自己处理一下了
         * 2：第二个问题，我们在下面解释
         **/
        for (GenericBeanDefinition genericBeanDefinition : list) {
            /**
             * 1、处理beanClass
             */
            Class<?> clazz = null;
            try {
                clazz = Thread.currentThread().getContextClassLoader().loadClass(genericBeanDefinition.getBeanClassName());
            } catch (ClassNotFoundException e) {
                log.error("bean class cant be load for beandefinition: {}",genericBeanDefinition);
                throw new RuntimeException();
            }

            genericBeanDefinition.setBeanClass(clazz);

            /**
             * 2、处理constructor问题，因为Object value = valueHolder.getValue();
             * 是Object类型，但这个实际是一个可变类型，当构造器参数为String类型时，这个Object就是	              * String类型的，当构造器参数类型为其他bean的引用时，这个object就是RuntimeBeanReference              * 的，
             * 因为fastjson把我的object转成jsonobject类型了，所以这里要手动搞成RuntimeBeanReference
             */
            ConstructorArgumentValues constructorArgumentValues = genericBeanDefinition.getConstructorArgumentValues();
            if (constructorArgumentValues.isEmpty()) {
                continue;
            }
            Map<Integer, ConstructorArgumentValues.ValueHolder> map = constructorArgumentValues.getIndexedArgumentValues();
            if (CollectionUtils.isEmpty(map)) {
                continue;
            }
            for (ConstructorArgumentValues.ValueHolder valueHolder : map.values()) {
                Object value = valueHolder.getValue();
                if (value instanceof JSONObject) {
                    JSONObject jsonObject = (JSONObject) value;
                    RuntimeBeanReference runtimeBeanReference = jsonObject.toJavaObject(RuntimeBeanReference.class);
                    valueHolder.setValue(runtimeBeanReference);
                }
            }
        }

        //这里new一个BeanNameGenerator，这是自带的
        setBeanNameGenerator(new AnnotationBeanNameGenerator());
        BeanNameGenerator beanNameGenerator = getBeanNameGenerator();
        // 获取BeanDefinitionRegistry，bean factory默认实现了BeanDefinitionRegistry
        BeanDefinitionRegistry registry = getRegistry();
        //注册bean definition到BeanDefinitionRegistry里面去
        for (GenericBeanDefinition genericBeanDefinition : list) {
            String beanName = beanNameGenerator.generateBeanName(genericBeanDefinition, registry);
            registry.registerBeanDefinition(beanName,genericBeanDefinition);
        }

        return list.size();
    }
}

收工了，测试一下

public class BootStrap {
    public static void main(String[] args) {
        // new一个我们的自定义json上下文
        ClassPathJsonApplicationContext context = new ClassPathJsonApplicationContext("beanDefinition.json");
        // getBean试一下
        TestControllerByConstructor bean = context.getBean(TestControllerByConstructor.class);
        System.out.println(bean);
    }
}

可以看到，已经注入进去了。没有什么问题。

总结

今天比较晚，写得也比较急，有问题的话，请大家务必指出，谢谢大家

源码地址：

https://gitee.com/ckl111/spring-boot-first-version-learn/tree/master/all-demo-in-spring-learning/spring-beans-json-extend