Spring-EntityResolver

docs/Spring/clazz/Spring-EntityResolver.md

@@ -0,0 +1,158 @@
+# EntityResolver
+- Author: [HuiFer](https://github.com/huifer)
+- 源码阅读仓库: [huifer-spring](https://github.com/huifer/spring-framework)
+- 源码路径: `org.xml.sax.EntityResolver`,非Spring类
+
+## DelegatingEntityResolver#resolveEntity
+- org.springframework.beans.factory.xml.DelegatingEntityResolver.resolveEntity
+```java
+    @Override
+    @Nullable
+    public InputSource resolveEntity(@Nullable String publicId, @Nullable String systemId)
+            throws SAXException, IOException {
+
+        if (systemId != null) {
+            if (systemId.endsWith(DTD_SUFFIX)) {
+                return this.dtdResolver.resolveEntity(publicId, systemId);
+            }
+            else if (systemId.endsWith(XSD_SUFFIX)) {
+                return this.schemaResolver.resolveEntity(publicId, systemId);
+            }
+        }
+
+        // Fall back to the parser's default behavior.
+        return null;
+    }
+
+```
+- 上述这段代码是针对xml进行校验
+```xml
+<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="http://www.springframework.org/schema/beans"
+       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
+```
+- 如上所示以`.xsd`结尾,应该执行` return this.schemaResolver.resolveEntity(publicId, systemId);`方法
+`http://www.springframework.org/schema/beans/spring-beans.xsd`
+- `org.springframework.beans.factory.xml.PluggableSchemaResolver.resolveEntity`
+## PluggableSchemaResolver#resolveEntity
+```java
+    @Override
+    @Nullable
+    public InputSource resolveEntity(@Nullable String publicId, @Nullable String systemId) throws IOException {
+        if (logger.isTraceEnabled()) {
+            logger.trace("Trying to resolve XML entity with public id [" + publicId +
+                    "] and system id [" + systemId + "]");
+        }
+
+        if (systemId != null) {
+            // 获取当前 systemId 对应的资源
+            // spring-framework\spring-beans\src\main\resources\org\springframework\beans\factory\xml\spring-beans.xsd
+            String resourceLocation = getSchemaMappings().get(systemId);
+            if (resourceLocation == null && systemId.startsWith("https:")) {
+                // Retrieve canonical http schema mapping even for https declaration
+                resourceLocation = getSchemaMappings().get("http:" + systemId.substring(6));
+            }
+            if (resourceLocation != null) {
+                // 加载 resourceLocation 转换成 Resource
+                Resource resource = new ClassPathResource(resourceLocation, this.classLoader);
+                try {
+                    // 读取
+                    InputSource source = new InputSource(resource.getInputStream());
+                    source.setPublicId(publicId);
+                    source.setSystemId(systemId);
+                    if (logger.isTraceEnabled()) {
+                        logger.trace("Found XML schema [" + systemId + "] in classpath: " + resourceLocation);
+                    }
+                    return source;
+                }
+                catch (FileNotFoundException ex) {
+                    if (logger.isDebugEnabled()) {
+                        logger.debug("Could not find XML schema [" + systemId + "]: " + resource, ex);
+                    }
+                }
+            }
+        }
+
+        // Fall back to the parser's default behavior.
+        return null;
+    }
+
+```
+
+![image-20200108081404857](/images/spring//image-20200108081404857.png)
+
+![image-20200108081623427](/images/spring//image-20200108081623427.png)
+
+得到本地路径，后续直接返回读取资源
+
+## BeansDtdResolver#resolveEntity
+
+创建一个Dtd的约束文件
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/dtd/spring-beans-2.0.dtd">
+
+</beans>
+```
+
+```java
+    @Override
+    @Nullable
+    public InputSource resolveEntity(@Nullable String publicId, @Nullable String systemId) throws IOException {
+        if (logger.isTraceEnabled()) {
+            logger.trace("Trying to resolve XML entity with public ID [" + publicId +
+                    "] and system ID [" + systemId + "]");
+        }
+
+        if (systemId != null && systemId.endsWith(DTD_EXTENSION)) {
+            int lastPathSeparator = systemId.lastIndexOf('/');
+            int dtdNameStart = systemId.indexOf(DTD_NAME, lastPathSeparator);
+            if (dtdNameStart != -1) {
+                // 获取静态变量组装成文件名称(spring-beans.dtd)
+                String dtdFile = DTD_NAME + DTD_EXTENSION;
+                if (logger.isTraceEnabled()) {
+                    logger.trace("Trying to locate [" + dtdFile + "] in Spring jar on classpath");
+                }
+                try {
+                    // 加载资源
+                    Resource resource = new ClassPathResource(dtdFile, getClass());
+                    InputSource source = new InputSource(resource.getInputStream());
+                    source.setPublicId(publicId);
+                    source.setSystemId(systemId);
+                    if (logger.isTraceEnabled()) {
+                        logger.trace("Found beans DTD [" + systemId + "] in classpath: " + dtdFile);
+                    }
+                    return source;
+                }
+                catch (FileNotFoundException ex) {
+                    if (logger.isDebugEnabled()) {
+                        logger.debug("Could not resolve beans DTD [" + systemId + "]: not found in classpath", ex);
+                    }
+                }
+            }
+        }
+
+        // Fall back to the parser's default behavior.
+        return null;
+    }
+
+```
+
+
+
+
+- systemId `https://www.springframework.org/dtd/spring-beans-2.0.dtd`
+
+![image-20200108082335031](/images/spring//image-20200108082335031.png)
+
+
+## 总结
+
+- DelegatingEntityResolver#resolveEntity,是对xml文档的校验前置步骤,根据`dtd`和`xsd`加载本地资源文件
+    `spring-framework\spring-beans\src\main\resources\org\springframework\beans\factory\xml\spring-beans.dtd`
+    `spring-framework\spring-beans\src\main\resources\org\springframework\beans\factory\xml\spring-beans.xsd`
+- `PluggableSchemaResolver`负责加载`xsd`文件
+- `BeansDtdResolver`负责加载`dtd`文件