Java自定义Spring配置标签
作者:「已注销」
引言:
在Sping中,一般使用<bean>这样的元素来配置一个bean,Spring在创建容器的时候会扫描这些配置,根据配置创建对象存放于容器中,然后我们再从容器中取出,或者在配置其他bean的时候作为属性注入。使用bean配置的一个限制是我们必须遵循配置文件的XML Schema定义,这在大多数情况下不会出现问题。但是在一些情况下,我们希望实现更为灵活的bean配置。Spring为此提供了 Custom tag Support,也称为Extensible XML Authoring。通过这个拓展点,我们可以灵活定制自己需要的配置格式。
例如,如果我们使用了责任链设计应用程序,那么我们可能希望用下面的方式来配置责任链:
<chain id="orderChain" class="foo.bar"> <handler> handler1</handler> <hadnler> handler2</handler> </chain>
档Spring创建容器时,扫描到这样的元素的时候,会根据我们事先的定义实例化一个责任链对象,并填充属性。因此,这种特殊的<chain>标签可以作为<bean>标签以外的另一种形式。借助Spring的Custome Tag,我们完全可以实现这样的bean配置。在产品级的应用框架中,可以实现更为复杂的定制标签元素。作为一个入门级别的介绍,我们定义一个用于配置日期格式化的一个类SimpleDateFormat。当然,使用传统的<bean>完全够用,我们这里只是作为例子。
一个HelloWorld例子:
定制标签的第一步是要定义标签元素的XML结构,也就是采用XSD来元素我们要定制的元素的结构时怎样的。
我们定义如下一个简单的XSD:
<?xml version="1.0" encoding="UTF-8"?> <xsd:schema xmlns="http://www.mycompany.com/schema/myns" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:beans="http://www.springframework.org/schema/beans" targetNamespace="http://www.mycompany.com/schema/myns" elementFormDefault="qualified" attributeFormDefault="unqualified"> <xsd:import namespace="http://www.springframework.org/schema/beans"/> <xsd:element name="dateformat"> <xsd:complexType> <xsd:complexContent> <xsd:extension base="beans:identifiedType"> <xsd:attribute name="lenient" type="xsd:boolean"/> <xsd:attribute name="pattern" type="xsd:string" use="required"/> </xsd:extension> </xsd:complexContent> </xsd:complexType> </xsd:element> </xsd:schema>
在这个XSD定义中,有一个标签叫dateformat,这就是我们用来替换bean标签的自定义标签。注意到我们导入了Spring本身的beans命名空间,并且在beans:identifiedType基础之上定义dateformat标签。也就是我们这个标签可以像<bean>标签一样拥有id属性。同时我们增加了两个属性lenient和pattern。这有点继承的味道。
定义完XSD之后,我们要告诉Spring遇到这样的标记(命名空间+元素名称)时,如何创建对象。Spring中,完成这个任务的是NamespaceHandler。因此我们需要提供一个NamespaceHandler实现来处理自定义的<dateformat>标签元素。
一个简单的实现如下:
package extensiblexml.customtag; import org.springframework.beans.factory.xml.NamespaceHandlerSupport; public class MyNamespaceHandler extends NamespaceHandlerSupport { public void init() { registerBeanDefinitionParser("dateformat", new SimpleDateFormatBeanDefinitionParser()); } }
我们在初始化方法中注册了一个Bean定义的解析器,这个解析器就是用来解析定制的配置标签的。
其实现如下:
package extensiblexml.customtag; import org.springframework.beans.factory.support.BeanDefinitionBuilder; import org.springframework.beans.factory.xml.AbstractSingleBeanDefinitionParser; import org.springframework.util.StringUtils; import org.w3c.dom.Element; import java.text.SimpleDateFormat; public class SimpleDateFormatBeanDefinitionParser extends AbstractSingleBeanDefinitionParser { protected Class<SimpleDateFormat> getBeanClass(Element element) { return SimpleDateFormat.class; } @SuppressWarnings("deprecation") protected void doParse(Element element, BeanDefinitionBuilder bean) { // this will never be null since the schema explicitly requires that a value be supplied String pattern = element.getAttribute("pattern"); bean.addConstructorArg(pattern); // this however is an optional property String lenient = element.getAttribute("lenient"); if (StringUtils.hasText(lenient)) { bean.addPropertyValue("lenient", Boolean.valueOf(lenient)); } } }
这个解析器的doParse中,实现了解析的具体逻辑,借助Spring提供的支持类,我们可以很轻松地完成解析。以上三个文件放在同一个目录下,即把XSD文件跟Java代码放在同一目录。编码完毕之后,还需要做一些配置工作。我们必须告诉Spring我们准备使用自定义的标签元素,告诉Spring如何解析元素,否则Spring没那么聪明。这里需要2个配置文件,在与代码根路径同一级别下,床垫一个叫META-INF的文件。并在里面创建名为spring.handlers和spring.schemas,用于告诉Spring自定义标签的文档结构以及解析它的类。两个文件内容分别如下:
spring.handlers:
http\://www.mycompany.com/schema/myns=extensiblexml.customtag.MyNamespaceHandler
等号的左边是XSD定义中的targetNamespace属性,右边是NamespaceHandler的全称限定名。
spring.schemas:
http\://www.mycompany.com/schema/myns/myns.xsd=extensiblexml/customtag/myns.xsd
然后像往常一样配置bean,作为简单的测试,我们定义一个bean:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:myns="http://www.mycompany.com/schema/myns" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.mycompany.com/schema/myns http://www.mycompany.com/schema/myns/myns.xsd" > <myns:dateformat id="defaultDateFormat" pattern="yyyy-MM-dd HH:mm" lenient="true" /> </beans>
在Eclipse中,整个项目结构如下图:
最后我们写个测试类测试一下能否工作:
package extensiblexml.customtag; import java.text.SimpleDateFormat; import java.util.Date; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Test { public static void main(String[] args) { ApplicationContext context = new ClassPathXmlApplicationContext( "beans.xml"); SimpleDateFormat format = (SimpleDateFormat) context .getBean("defaultDateFormat"); System.out.println(format.format(new Date())); } }
一切正常,输出如下:
更实用的例子
第一个例子主要是为了举例,在实际中用处不大,我们接着来看一个更复杂的自定义标签。我们自定义一个<fileList>标签,当Spring扫描到这个标签的时候,创建一个指定目录下的File类的集合。另外,可以使用<fileFilter>对该目录的文件进行过滤。
如下:
<core-commons:fileList id="xmlList" directory="src/extensiblexml/example"> <core-commons:fileFilter> <bean class="org.apache.commons.io.filefilter.RegexFileFilter"> <constructor-arg value=".*.java" /> </bean> </core-commons:fileFilter> </core-commons:fileList>
上面的bean定义中,我们从“src/extensible/example”目录中筛选出java源码文件。
使用下面的测试迭代输出文件名:
@SuppressWarnings("unchecked") List<File> fileList = (List<File>) context.getBean("xmlList"); for (File file : fileList) { System.out.println(file.getName()); }
输出结果如下:
根据第一个例子中的步骤,各部分配置及代码如下:
core-commons-1.0.xsd:
<?xml version="1.0" encoding="UTF-8"?> <xsd:schema xmlns="http://www.example.com/schema/core-commons-1.0" targetNamespace="http://www.example.com/schema/core-commons-1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:beans="http://www.springframework.org/schema/beans" elementFormDefault="qualified" attributeFormDefault="unqualified" version="1.0"> <xsd:import namespace="http://www.springframework.org/schema/beans" schemaLocation="http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"/> <xsd:element name="fileList"> <xsd:complexType> <xsd:complexContent> <xsd:extension base="beans:identifiedType"> <xsd:sequence> <xsd:element ref="fileFilter" minOccurs="0" maxOccurs="1"/> <xsd:element ref="fileList" minOccurs="0" maxOccurs="unbounded"/> </xsd:sequence> <xsd:attribute name="directory" type="xsd:string"/> <xsd:attribute name="scope" type="xsd:string"/> </xsd:extension> </xsd:complexContent> </xsd:complexType> </xsd:element> <xsd:element name="fileFilter"> <xsd:complexType> <xsd:complexContent> <xsd:extension base="beans:identifiedType"> <xsd:group ref="limitedType"/> <xsd:attribute name="scope" type="xsd:string"/> </xsd:extension> </xsd:complexContent> </xsd:complexType> </xsd:element> <xsd:group name="limitedType"> <xsd:sequence> <xsd:choice minOccurs="1" maxOccurs="unbounded"> <xsd:element ref="beans:bean"/> <xsd:element ref="beans:ref"/> <xsd:element ref="beans:idref"/> <xsd:element ref="beans:value"/> <xsd:any minOccurs="0"/> </xsd:choice> </xsd:sequence> </xsd:group> </xsd:schema>
CoreNamespaceHandler.java:
package extensiblexml.example; import org.springframework.beans.factory.xml.NamespaceHandlerSupport; public class CoreNamespaceHandler extends NamespaceHandlerSupport { @Override public void init() { this.registerBeanDefinitionParser("fileList", new FileListDefinitionParser()); this.registerBeanDefinitionParser("fileFilter", new FileFilterDefinitionParser()); } }
FileListDefinitionParser.java:
public class FileListDefinitionParser extends AbstractSingleBeanDefinitionParser { /** * The bean that is created for this tag element * * @param element The tag element * @return A FileListFactoryBean */ @Override protected Class<?> getBeanClass(Element element) { return FileListFactoryBean.class; } /** * Called when the fileList tag is to be parsed * * @param element The tag element * @param ctx The context in which the parsing is occuring * @param builder The bean definitions build to use */ @Override protected void doParse(Element element, ParserContext ctx, BeanDefinitionBuilder builder) { // Set the directory property builder.addPropertyValue("directory", element.getAttribute("directory")); // Set the scope builder.setScope(element.getAttribute("scope")); // We want any parsing to occur as a child of this tag so we need to make // a new one that has this as it's owner/parent ParserContext nestedCtx = new ParserContext(ctx.getReaderContext(), ctx.getDelegate(), builder.getBeanDefinition()); // Support for filters Element exclusionElem = DomUtils.getChildElementByTagName(element, "fileFilter"); if (exclusionElem != null) { // Just make a new Parser for each one and let the parser do the work FileFilterDefinitionParser ff = new FileFilterDefinitionParser(); builder.addPropertyValue("filters", ff.parse(exclusionElem, nestedCtx)); } // Support for nested fileList List<Element> fileLists = DomUtils.getChildElementsByTagName(element, "fileList"); // Any objects that created will be placed in a ManagedList // so Spring does the bulk of the resolution work for us ManagedList<Object> nestedFiles = new ManagedList<Object>(); if (fileLists.size() > 0) { // Just make a new Parser for each one and let them do the work FileListDefinitionParser fldp = new FileListDefinitionParser(); for (Element fileListElem : fileLists) { nestedFiles.add(fldp.parse(fileListElem, nestedCtx)); } } // Support for other tags that return File (value will be converted to file) try { // Go through any other tags we may find. This does not mean we support // any tag, we support only what parseLimitedList will process NodeList nl = element.getChildNodes(); for (int i=0; i<nl.getLength(); i++) { // Parse each child tag we find in the correct scope but we // won't support custom tags at this point as it coudl destablize things DefinitionParserUtil.parseLimitedList(nestedFiles, nl.item(i), ctx, builder.getBeanDefinition(), element.getAttribute("scope"), false); } } catch (Exception e) { throw new RuntimeException(e); } // Set the nestedFiles in the properties so it is set on the FactoryBean builder.addPropertyValue("nestedFiles", nestedFiles); } public static class FileListFactoryBean implements FactoryBean<Collection<File>> { String directory; private Collection<FileFilter> filters; private Collection<File> nestedFiles; @Override public Collection<File> getObject() throws Exception { // These can be an array list because the directory will have unique's and the nested is already only unique's Collection<File> files = new ArrayList<File>(); Collection<File> results = new ArrayList<File>(0); if (directory != null) { // get all the files in the directory File dir = new File(directory); File[] dirFiles = dir.listFiles(); if (dirFiles != null) { files = Arrays.asList(dirFiles); } } // If there are any files that were created from the nested tags, // add those to the list of files if (nestedFiles != null) { files.addAll(nestedFiles); } // If there are filters we need to go through each filter // and see if the files in the list pass the filters. // If the files does not pass any one of the filters then it // will not be included in the list if (filters != null) { boolean add; for (File f : files) { add = true; for (FileFilter ff : filters) { if (!ff.accept(f)) { add = false; break; } } if (add) results.add(f); } return results; } return files; } @Override public Class<?> getObjectType() { return Collection.class; } @Override public boolean isSingleton() { return false; } public void setDirectory(String dir) { this.directory = dir; } public void setFilters(Collection<FileFilter> filters) { this.filters = filters; } /** * What we actually get from the processing of the nested tags * is a collection of files within a collection so we flatten it and * only keep the uniques */ public void setNestedFiles(Collection<Collection<File>> nestedFiles) { this.nestedFiles = new HashSet<File>(); // keep the list unique for (Collection<File> nested : nestedFiles) { this.nestedFiles.addAll(nested); } } } }
FileFilterDefinitionParser.java
public class FileFilterDefinitionParser extends AbstractSingleBeanDefinitionParser { /** * The bean that is created for this tag element * * @param element The tag element * @return A FileFilterFactoryBean */ @Override protected Class<?> getBeanClass(Element element) { return FileFilterFactoryBean.class; } /** * Called when the fileFilter tag is to be parsed * * @param element The tag element * @param ctx The context in which the parsing is occuring * @param builder The bean definitions build to use */ @Override protected void doParse(Element element, ParserContext ctx, BeanDefinitionBuilder builder) { // Set the scope builder.setScope(element.getAttribute("scope")); try { // All of the filters will eventually end up in this list // We use a 'ManagedList' and not a regular list because anything // placed in a ManagedList object will support all of Springs // functionalities and scopes for us, we dont' have to code anything // in terms of reference lookups, EL, etc ManagedList<Object> filters = new ManagedList<Object>(); // For each child node of the fileFilter tag, parse it and place it // in the filtes list NodeList nl = element.getChildNodes(); for (int i=0; i<nl.getLength(); i++) { DefinitionParserUtil.parseLimitedList(filters, nl.item(i), ctx, builder.getBeanDefinition(), element.getAttribute("scope")); } // Add the filtes to the list of properties (this is applied // to the factory beans setFilters below) builder.addPropertyValue("filters", filters); } catch (Exception e) { throw new RuntimeException(e); } } public static class FileFilterFactoryBean implements FactoryBean<Collection<FileFilter>> { private final List<FileFilter> filters = new ArrayList<FileFilter>(); @Override public Collection<FileFilter> getObject() throws Exception { return filters; } @Override public Class<?> getObjectType() { return Collection.class; } @Override public boolean isSingleton() { return false; } /** * Go through the list of filters and convert the String ones * (the ones that were set with <value> and make them NameFileFilters */ public void setFilters(Collection<Object> filterList) { for (Object o : filterList) { if (o instanceof String) { filters.add(new NameFileFilter(o.toString())); } else if (o instanceof FileFilter) { filters.add((FileFilter)o); } } } } }
DefinitionParserUtil.java:
package extensiblexml.example; import org.springframework.beans.factory.config.BeanDefinition; import org.springframework.beans.factory.config.BeanDefinitionHolder; import org.springframework.beans.factory.support.BeanDefinitionReaderUtils; import org.springframework.beans.factory.support.DefaultListableBeanFactory; import org.springframework.beans.factory.support.ManagedList; import org.springframework.beans.factory.xml.BeanDefinitionParserDelegate; import org.springframework.beans.factory.xml.ParserContext; import org.springframework.expression.Expression; import org.springframework.expression.ExpressionParser; import org.springframework.expression.spel.standard.SpelExpressionParser; import org.w3c.dom.Element; import org.w3c.dom.Node; public class DefinitionParserUtil { /** * Parses the children of the passed in ParentNode for the following tags: * <br/> * value * ref * idref * bean * property * *custom* * <p/> * * The value tag works with Spring EL even in a Spring Batch scope="step" * * @param objects The list of resultings objects from the parsing (passed in for recursion purposes) * @param parentNode The node who's children should be parsed * @param ctx The ParserContext to use * @param parentBean The BeanDefinition of the bean who is the parent of the parsed bean * (i.e. the Bean that is the parentNode) * @param scope The scope to execute in. Checked if 'step' to provide Spring EL * support in a Spring Batch env * @throws Exception */ public static void parseLimitedList(ManagedList<Object> objects, Node node, ParserContext ctx, BeanDefinition parentBean, String scope) throws Exception { parseLimitedList(objects, node, ctx, parentBean, scope, true); } /** * Parses the children of the passed in ParentNode for the following tags: * <br/> * value * ref * idref * bean * property * *custom* * <p/> * * The value tag works with Spring EL even in a Spring Batch scope="step" * * @param objects The list of resultings objects from the parsing (passed in for recursion purposes) * @param parentNode The node who's children should be parsed * @param ctx The ParserContext to use * @param parentBean The BeanDefinition of the bean who is the parent of the parsed bean * (i.e. the Bean that is the parentNode) * @param scope The scope to execute in. Checked if 'step' to provide Spring EL * support in a Spring Batch env * @param supportCustomTags Should we support custom tags within our tags? * @throws Exception */ @SuppressWarnings("deprecation") public static void parseLimitedList(ManagedList<Object> objects, Node node, ParserContext ctx, BeanDefinition parentBean, String scope, boolean supportCustomTags) throws Exception { // Only worry about element nodes if (node.getNodeType() == Node.ELEMENT_NODE) { Element elem = (Element)node; String tagName = node.getLocalName(); if (tagName.equals("value")) { String val = node.getTextContent(); // to get around an issue with Spring Batch not parsing Spring EL // we will do it for them if (scope.equals("step") && (val.startsWith("#{") && val.endsWith("}")) && (!val.startsWith("#{jobParameters")) ) { // Set up a new EL parser ExpressionParser parser = new SpelExpressionParser(); // Parse the value Expression exp = parser.parseExpression(val.substring(2, val.length()-1)); // Place the results in the list of created objects objects.add(exp.getValue()); } else { // Otherwise, just treat it as a normal value tag objects.add(val); } } // Either of these is a just a lookup of an existing bean else if (tagName.equals("ref") || tagName.equals("idref")) { objects.add(ctx.getRegistry().getBeanDefinition(node.getTextContent())); } // We need to create the bean else if (tagName.equals("bean")) { // There is no quick little util I could find to create a bean // on the fly programmatically in Spring and still support all // Spring functionality so basically I mimic what Spring actually // does but on a smaller scale. Everything Spring allows is // still supported // Create a factory to make the bean DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory(); // Set up a parser for the bean BeanDefinitionParserDelegate pd = new BeanDefinitionParserDelegate(ctx.getReaderContext()); // Parse the bean get its information, now in a DefintionHolder BeanDefinitionHolder bh = pd.parseBeanDefinitionElement(elem, parentBean); // Register the bean will all the other beans Spring is aware of BeanDefinitionReaderUtils.registerBeanDefinition(bh, beanFactory); // Get the bean from the factory. This will allows Spring // to do all its work (EL processing, scope, etc) and give us // the actual bean itself Object bean = beanFactory.getBean(bh.getBeanName()); objects.add(bean); } /* * This is handled a bit differently in that it actually sets the property * on the parent bean for us based on the property */ else if (tagName.equals("property")) { BeanDefinitionParserDelegate pd = new BeanDefinitionParserDelegate(ctx.getReaderContext()); // This method actually set eh property on the parentBean for us so // we don't have to add anything to the objects object pd.parsePropertyElement(elem, parentBean); } else if (supportCustomTags) { // handle custom tag BeanDefinitionParserDelegate pd = new BeanDefinitionParserDelegate(ctx.getReaderContext()); BeanDefinition bd = pd.parseCustomElement(elem, parentBean); objects.add(bd); } } } }
spring.schemas
http\://www.mycompany.com/schema/myns/myns.xsd=extensiblexml/customtag/myns.xsd
http\://www.example.com/schema/core-commons-1.0.xsd=extensiblexml/example/core-commons-1.0.xsd
spring.handlers
http\://www.mycompany.com/schema/myns=extensiblexml.customtag.MyNamespaceHandler
http\://www.example.com/schema/core-commons-1.0=extensiblexml.example.CoreNamespaceHandler
小结:
要自定义Spring的配置标签,需要一下几个步骤:
- 使用XSD定义XML配置中标签元素的结构(myns.XSD)
- 提供该XSD命名空间的处理类,它可以处理多个标签定义(MyNamespaceHandler.java)
- 为每个标签元素的定义提供解析类。(SimpleDateFormatBeanDefinitionParser.java)
- 两个特殊文件通知Spring使用自定义标签元素(spring.handlers 和spring.schemas)
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