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：
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：
