Java自定義Spring配置標簽
引言：
在Sping中，一般使用<bean>這樣的元素來配置一個bean，Spring在創建容器的時候會掃描這些配置，根據配置創建對象存放於容器中，然後我們再從容器中取出，或者在配置其他bean的時候作為屬性註入。使用bean配置的一個限制是我們必須遵循配置文件的XML Schema定義，這在大多數情況下不會出現問題。但是在一些情況下，我們希望實現更為靈活的bean配置。Spring為此提供瞭 Custom tag Support，也稱為Extensible XML Authoring。通過這個拓展點，我們可以靈活定制自己需要的配置格式。
例如，如果我們使用瞭責任鏈設計應用程序，那麼我們可能希望用下面的方式來配置責任鏈：
<chain id="orderChain" class="foo.bar">
<handler> handler1</handler>
<hadnler> handler2</handler>
</chain>
檔Spring創建容器時，掃描到這樣的元素的時候，會根據我們事先的定義實例化一個責任鏈對象，並填充屬性。因此，這種特殊的<chain>標簽可以作為<bean>標簽以外的另一種形式。借助Spring的Custome Tag，我們完全可以實現這樣的bean配置。在產品級的應用框架中，可以實現更為復雜的定制標簽元素。作為一個入門級別的介紹，我們定義一個用於配置日期格式化的一個類SimpleDateFormat。當然，使用傳統的<bean>完全夠用，我們這裡隻是作為例子。
一個HelloWorld例子：
定制標簽的第一步是要定義標簽元素的XML結構，也就是采用XSD來元素我們要定制的元素的結構時怎樣的。
我們定義如下一個簡單的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>
在這個XSD定義中，有一個標簽叫dateformat，這就是我們用來替換bean標簽的自定義標簽。註意到我們導入瞭Spring本身的beans命名空間，並且在beans:identifiedType基礎之上定義dateformat標簽。也就是我們這個標簽可以像<bean>標簽一樣擁有id屬性。同時我們增加瞭兩個屬性lenient和pattern。這有點繼承的味道。
定義完XSD之後，我們要告訴Spring遇到這樣的標記（命名空間+元素名稱）時，如何創建對象。Spring中，完成這個任務的是NamespaceHandler。因此我們需要提供一個NamespaceHandler實現來處理自定義的<dateformat>標簽元素。
一個簡單的實現如下：
package extensiblexml.customtag;
import org.springframework.beans.factory.xml.NamespaceHandlerSupport;
public class MyNamespaceHandler extends NamespaceHandlerSupport {
public void init() {
registerBeanDefinitionParser("dateformat",
new SimpleDateFormatBeanDefinitionParser());
}
}
我們在初始化方法中註冊瞭一個Bean定義的解析器，這個解析器就是用來解析定制的配置標簽的。
其實現如下：
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));
}
}
}
這個解析器的doParse中，實現瞭解析的具體邏輯，借助Spring提供的支持類，我們可以很輕松地完成解析。以上三個文件放在同一個目錄下，即把XSD文件跟Java代碼放在同一目錄。編碼完畢之後，還需要做一些配置工作。我們必須告訴Spring我們準備使用自定義的標簽元素，告訴Spring如何解析元素，否則Spring沒那麼聰明。這裡需要2個配置文件，在與代碼根路徑同一級別下，床墊一個叫META-INF的文件。並在裡面創建名為spring.handlers和spring.schemas,用於告訴Spring自定義標簽的文檔結構以及解析它的類。兩個文件內容分別如下：
spring.handlers:
http\://www.mycompany.com/schema/myns=extensiblexml.customtag.MyNamespaceHandler
等號的左邊是XSD定義中的targetNamespace屬性，右邊是NamespaceHandler的全稱限定名。
spring.schemas:
http\://www.mycompany.com/schema/myns/myns.xsd=extensiblexml/customtag/myns.xsd
然後像往常一樣配置bean，作為簡單的測試，我們定義一個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，整個項目結構如下圖：
最後我們寫個測試類測試一下能否工作：
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，輸出如下：
更實用的例子
第一個例子主要是為瞭舉例，在實際中用處不大，我們接著來看一個更復雜的自定義標簽。我們自定義一個<fileList>標簽，當Spring掃描到這個標簽的時候，創建一個指定目錄下的File類的集合。另外，可以使用<fileFilter>對該目錄的文件進行過濾。
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定義中，我們從“src/extensible/example”目錄中篩選出java源碼文件。
使用下面的測試迭代輸出文件名：
@SuppressWarnings("unchecked")
List<File> fileList = (List<File>) context.getBean("xmlList");
for (File file : fileList) {
System.out.println(file.getName());
}
輸出結果如下：
根據第一個例子中的步驟，各部分配置及代碼如下：
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
小結：
要自定義Spring的配置標簽，需要一下幾個步驟：
- 使用XSD定義XML配置中標簽元素的結構(myns.XSD)
- 提供該XSD命名空間的處理類，它可以處理多個標簽定義(MyNamespaceHandler.java)
- 為每個標簽元素的定義提供解析類。(SimpleDateFormatBeanDefinitionParser.java)
- 兩個特殊文件通知Spring使用自定義標簽元素（spring.handlers 和spring.schemas)
到此這篇關於Java自定義Spring配置標簽的文章就介紹到這瞭,更多相關Java Spring配置標簽內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet！
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