Java依赖注入容器超详细全面讲解
目录
- 一、依赖注入Dependency Injection
- 二、解析
- 2.1 典型的配置文件
- 2.2 配置文件所对应的Java类
- 2.3 定义解析器
- 三、bean工厂(根据bean定义创建bean对象)
- 四、DI容器(上下文)
- 4.1 容器接口
- 4.2 XML容器
- 五、使用DI容器
一、依赖注入Dependency Injection
DI容器底层最基本的设计思路就是基于工厂模式。
DI容器的核心功能:配置解析、对象创建、对象声明周期。
完整的代码:Dependency Injection。
二、解析
通过配置,让DI容器知道要创建哪些对象。
DI容器读取文件,根据配置文件来创建对象。
2.1 典型的配置文件
下面是一个典型的配置文件:
<?xml version="1.0" encoding="UTF-8"?> <beans> <bean id="productInfo" class="com.hef.review.designpatterns.creational.di.beans.ProductInfo"> <constructor-arg type="String" value="P01"/> <constructor-arg type="int" value="200"/> </bean> <bean id="productSell" class="com.hef.review.designpatterns.creational.di.beans.ProductSell"> <constructor-arg ref="productInfo"/> </bean> </beans>
2.2 配置文件所对应的Java类
public class ProductInfo { private String productName; private int productVersion; public ProductInfo(String productName, int productVersion) { this.productName = productName; this.productVersion = productVersion; } // 省略 getter 和 setter } public class ProductSell { private ProductInfo productInfo; public ProductSell(ProductInfo productInfo) { this.productInfo = productInfo; } public void sell() { System.out.println("销售:" + productInfo); } // 省略 getter 和 setter }
2.3 定义解析器
Bean定义:
/** * Bean定义 */ public class BeanDefinition { private String id; private String className; private List<ConstructorArg> constructorArgs = new ArrayList<>(); private Scope scope = Scope.SINGLETON; private boolean lazyInit = false; public BeanDefinition(){} public BeanDefinition(String id, String className) { this.id = id; this.className = className; } // 省略getter 和 setter方法 }
配置解析接口:
/** * 将XML配置解析成 Bean定义 */ public interface BeanConfigParser { /** * 解析Bean定义 * @param in * @return */ List<BeanDefinition> parse(InputStream in); }
XML解析实现(使用Java自带的DOM解析类库):
/** * 解析XML,使用JDK自带的DOM解析类库 */ public class BeanXmlConfigParser implements BeanConfigParser { /** * 根据流进行解析 * @param in * @return */ @Override public List<BeanDefinition> parse(InputStream in) { try { List<BeanDefinition> result = new ArrayList<>(); DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance(); DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder(); Document doc = documentBuilder.parse(in); doc.getDocumentElement().normalize(); NodeList beanList = doc.getElementsByTagName("bean"); for (int i = 0; i < beanList.getLength(); i++) { Node node = beanList.item(i); if (!Objects.equals(node.getNodeType(), Node.ELEMENT_NODE)) continue; Element element = (Element) node; BeanDefinition beanDefinition = new BeanDefinition(element.getAttribute("id"), element.getAttribute("class")); if (element.hasAttribute("scope") && StringUtils.equals(element.getAttribute("scope"), BeanDefinition.Scope.PROTOTYPE.name())) { beanDefinition.setScope(BeanDefinition.Scope.PROTOTYPE); } if (element.hasAttribute("lazy-init") && Boolean.valueOf(element.getAttribute("lazy-init"))) { beanDefinition.setLazyInit(true); } List<BeanDefinition.ConstructorArg> constructorArgs = createConstructorArgs(element); if (CollectionUtils.isNotEmpty(constructorArgs)) { beanDefinition.setConstructorArgs(constructorArgs); } result.add(beanDefinition); } return result; }catch (Exception e) { throw new RuntimeException(e); } } /** * 创建构造函数 * @param element * @return */ private List<BeanDefinition.ConstructorArg> createConstructorArgs(Element element) { List<BeanDefinition.ConstructorArg> result = new ArrayList<>(); NodeList nodeList = element.getElementsByTagName("constructor-arg"); if (nodeList.getLength()==0) return result; for (int i = 0; i < nodeList.getLength(); i++) { Node node = nodeList.item(i); if (!Objects.equals(node.getNodeType(), Node.ELEMENT_NODE)) continue; Element ele = (Element) node; BeanDefinition.ConstructorArg arg = new BeanDefinition.ConstructorArg(); if (ele.hasAttribute("type") && StringUtils.isNoneBlank(ele.getAttribute("type"))) { String type = ele.getAttribute("type"); String value = ele.getAttribute("value"); arg.setType(fetchClassType(type)); arg.setArg(fetchArgValue(type, value)); arg.setRef(false); }else if (ele.hasAttribute("ref")) { arg.setRef(true); arg.setArg(ele.getAttribute("ref")); } result.add(arg); } return result; } /** * 获取构造函数 参数的值 * @param typeValue * @param value * @return */ private Object fetchArgValue(String typeValue, String value) { if (StringUtils.equals(typeValue, "int") || StringUtils.contains(typeValue, "Integer")) { return Integer.parseInt(value); }else if (StringUtils.contains(typeValue, "String")) { return value; } else { throw new RuntimeException("未知类型"); } } /** * 获取构造函数的类型, 注意原始类型的 Class表示 * @param typeValue * @return */ private Class<?> fetchClassType(String typeValue) { if (StringUtils.equals(typeValue, "int")){ return Integer.TYPE; } else if(StringUtils.contains(typeValue, "Integer")) { return Integer.class; }else if (StringUtils.contains(typeValue, "String")) { return String.class; } else { throw new RuntimeException("未知类型"); } } }
三、bean工厂(根据bean定义创建bean对象)
根据bean工厂创建bean的对象:
/** * bean工厂:利用反射, 根据Bean定义创建Bean对象 */ public class BeansFactory { private ConcurrentHashMap<String, Object> singletonObjects = new ConcurrentHashMap<>(); private ConcurrentHashMap<String, BeanDefinition> beanDefinitions = new ConcurrentHashMap<>(); /** * 向Bean工厂中,添加Bean定义 * @param beanDefinitionList */ public void addBeanDefinitions(List<BeanDefinition> beanDefinitionList) { for (BeanDefinition beanDefinition : beanDefinitionList) { this.beanDefinitions.putIfAbsent(beanDefinition.getId(), beanDefinition); } for (BeanDefinition beanDefinition : beanDefinitionList) { if (!beanDefinition.isLazyInit() && beanDefinition.isSingleton()) { singletonObjects.put(beanDefinition.getId(), createBean(beanDefinition)); } } } /** * 根据beanId获取Bean对象 * @param beanId * @return */ public Object getBean(String beanId) { BeanDefinition beanDefinition = beanDefinitions.get(beanId); checkState(Objects.nonNull(beanDefinition), "Bean is not defined:" + beanId); return createBean(beanDefinition); } /** * 根据Bean定义创建Bean对象 * @param beanDefinition * @return */ private Object createBean(BeanDefinition beanDefinition) { if (beanDefinition.isSingleton() && singletonObjects.containsKey(beanDefinition.getId())) { return singletonObjects.get(beanDefinition.getId()); } Object result = null; try { Class<?> beanClass = Class.forName(beanDefinition.getClassName()); List<BeanDefinition.ConstructorArg> constructorArgs = beanDefinition.getConstructorArgs(); if (CollectionUtils.isEmpty(constructorArgs)) { result = beanClass.newInstance(); } else { Class[] argClasses = new Class[constructorArgs.size()]; Object[] argObjects = new Object[constructorArgs.size()]; for (int k = 0; k < constructorArgs.size(); k++) { BeanDefinition.ConstructorArg arg = constructorArgs.get(k); if (!arg.isRef()) { argClasses[k] = arg.getType(); argObjects[k] = arg.getArg(); } else { BeanDefinition refBeanDefinition = beanDefinitions.get(arg.getArg()); checkState(Objects.nonNull(refBeanDefinition), "Bean is not defined: " + arg.getArg()); argClasses[k] = Class.forName(refBeanDefinition.getClassName()); argObjects[k] = createBean(refBeanDefinition); } } result = beanClass.getConstructor(argClasses).newInstance(argObjects); } if (Objects.nonNull(result) && beanDefinition.isSingleton()) { singletonObjects.putIfAbsent(beanDefinition.getId(), result); return singletonObjects.get(beanDefinition.getId()); } return result; }catch (Exception e) { throw new RuntimeException(e); } } }
四、DI容器(上下文)
4.1 容器接口
/** * DI容器接口 */ public interface ApplicationContext { Object getBean(String beanId); void loadBeanDefinitions(String configLocation); }
4.2 XML容器
/** * XML DI容器上下文 */ public class ClassPathXmlApplicationContext implements ApplicationContext { private BeansFactory beansFactory; private BeanConfigParser beanConfigParser; public ClassPathXmlApplicationContext(String configLocation) { this.beansFactory = new BeansFactory(); this.beanConfigParser = new BeanXmlConfigParser(); loadBeanDefinitions(configLocation); } /** * 根据配置文件路径,把XML文件 解析成 bean定义对象 * @param configLocation */ public void loadBeanDefinitions(String configLocation) { try (InputStream in = this.getClass().getClassLoader().getResourceAsStream(configLocation)) { if (in==null) { throw new RuntimeException("未发现配置文件:" + configLocation); } List<BeanDefinition> beanDefinitionList = beanConfigParser.parse(in); beansFactory.addBeanDefinitions(beanDefinitionList); } catch (IOException e) { throw new RuntimeException(e); } } /** * 从Bean工厂获取Bean对象 * @param beanId * @return */ @Override public Object getBean(String beanId) { return beansFactory.getBean(beanId); } }
五、使用DI容器
/** * 使用DI容器,从获取中获取Bean对象 */ public class Demo { public static void main(String[] args) { // testReadResourceXML(); // testParseXML(); ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml"); Object productInfo = context.getBean("productInfo"); System.out.println(productInfo); ProductSell productSell = (ProductSell)context.getBean("productSell"); productSell.sell(); } // 省略 testReadResourceXML() 和 testParseXML() }
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