寫在前面的話

相關背景及資源：

曹工說Spring Boot原始碼系列開講了（1）-- Bean Definition到底是什麼，附spring思維導圖分享

工程程式碼地址 思維導圖地址

工程結構圖：

大體思路

總體來說，bean definition是什麼，我們前面幾講，說了個大概了；目前，我們將聚焦於怎麼獲取bean definition。

我們這次做個實驗，就是將bean definition（一共兩個bean，有依賴關係，依賴是手動指定的）定義在json檔案內，然後自定義一個applicationcontext，從該檔案內讀取bean definiton，最後我們測試下是否能work。

注意哈，這裡的依賴，依然和前面講的一樣，都是手動指定依賴，類似@Autowired這種，還會放到後面才會講，開車也要先學手動檔嘛，是伐？

建議大家直接拖原始碼下來看：

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

定義json檔案

json檔案內，要表達bean definition，按照我們前面說的，基本就包括幾個必要的就行了，比如beanClassName。但我這裡還是展示一個完整的，但我也是用fastjson

// 這裡獲取到的bean definition的實際型別是 GenericBeanDefiniton，所以序列化出來的的json，就是一個
// GenericBeanDefiniton集合的json
List<BeanDefinition> beanDefinitionList = factory.getBeanDefinitionList()
JSON.toJSONString(beanDefinitionList)

json檔案內容如下：

[
  {
    "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
  }
]
 

大家可能看得有點懵，其實換成xml，就是類似下面這樣的：

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

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

擴充套件 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 {
        //其實主要內容和xmlapplicationcontext是一樣的，主要就是下面這行不一樣，new了一個json reader
        JsonBeanDefinitionReader beanDefinitionReader = new JsonBeanDefinitionReader(beanFactory);

        beanDefinitionReader.setEnvironment(this.getEnvironment());
        beanDefinitionReader.setResourceLoader(this);
        // 這裡通過json bean definiton reader去讀取bean definition
        loadBeanDefinitions(beanDefinitionReader);
    }

    /**
     *通過json bean definiton reader去讀取bean definition
     **/
    protected void loadBeanDefinitions(JsonBeanDefinitionReader reader) throws BeansException, IOException {
        // 這裡獲取json檔案的path，這個location是在new ClassPathJsonApplicationContext時傳進來的
        String[] configResources = getConfigLocations();
        if (configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }
    }

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

    /**
     * 這裡一模一樣，不需要任何變化
     **/
    public ClassPathJsonApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
            throws BeansException {

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

擴充套件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.*;

/**
 * 類似
 * {@link org.springframework.beans.factory.xml.XmlBeanDefinitionReader}
 * 只是本類是去json檔案裡讀取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開始
        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結束
        
        
        //這裡的encodedResource.getResource()就是我們的json檔案，這裡通過spring core裡面的一個工具類讀取為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：因為GenericBeanDefinition，只有setBeanClassName，所以bean反序列化時，只序列化了這個字        * 段；實際我們知道，beanClass很重要，所以我們只能自己處理一下了
         * 2：第二個問題，我們在下面解釋
         **/
        for (GenericBeanDefinition genericBeanDefinition : list) {
            /**
             * 1、處理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、處理constructor問題，因為Object value = valueHolder.getValue();
             * 是Object型別，但這個實際是一個可變型別，當構造器引數為String型別時，這個Object就是                 * String型別的，當構造器引數型別為其他bean的引用時，這個object就是RuntimeBeanReference              * 的，
             * 因為fastjson把我的object轉成jsonobject型別了，所以這裡要手動搞成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);
                }
            }
        }
        
        //這裡new一個BeanNameGenerator，這是自帶的
        setBeanNameGenerator(new AnnotationBeanNameGenerator());
        BeanNameGenerator beanNameGenerator = getBeanNameGenerator();
        // 獲取BeanDefinitionRegistry，bean factory預設實現了BeanDefinitionRegistry
        BeanDefinitionRegistry registry = getRegistry();
        //註冊bean definition到BeanDefinitionRegistry裡面去
        for (GenericBeanDefinition genericBeanDefinition : list) {
            String beanName = beanNameGenerator.generateBeanName(genericBeanDefinition, registry);
            registry.registerBeanDefinition(beanName,genericBeanDefinition);
        }

        return list.size();
    }
}

收工了，測試一下

public class BootStrap {
    public static void main(String[] args) {
        // new一個我們的自定義json上下文
        ClassPathJsonApplicationContext context = new ClassPathJsonApplicationContext("beanDefinition.json");
        // getBean試一下
        TestControllerByConstructor bean = context.getBean(TestControllerByConstructor.class);
        System.out.println(bean);
    }
}

可以看到，已經注入進去了。沒有什麼問題。

總結

今天比較晚，寫得也比較急，有問題的話，請大家務必指出，謝謝大家

原始碼地址：

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