通过velocity模板和Hibernate sql-query的实现动态hql

在开发的时候，很多时候都遇到过需要动态拼写SQL，有的是在配置文件中写SQL，有的是在Java代码中拼写SQL，以配置文件拼SQL的可以拿IBatis为代表，但是很多时候是使用Hibernate的，这个时候就想要是Hibernate能像IBatis那样写就好了。

原创不易，转载请注明出处：通过velocity模板和Hibernate sql-query的实现动态hql

代码下载：http://www.zuidaima.com/share/1723627800005632.htm

这个时候就想到了模板语言和配置文件的结合。模板引擎可以选择Velocity，简单而不失强大，配置文件可以模仿Hibernate的sql-query 的XML文件。

Sql-query的示例代码如下(SQL or HQL)：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dynamic-hibernate PUBLIC "-//ANYFRAME//DTD DYNAMIC-HIBERNATE//EN"
"http://www.anyframejava.org/dtd/anyframe-dynamic-hibernate-mapping-4.0.dtd">
<dynamic-hibernate>
    <query name="selectUserSQL">
        <![CDATA[
            SELECT  USER_ID,NAME
            FROM zuidaima_com_user Where 1=1
            #if($name && $name.length() > 1)
             AND name =:name
            #end
    ]]>
    </query>
    <query name="selectUserHQL">
    <![CDATA[
         FROM zuidaima_com_users
        Where 1=1
            #if($name && $name.length() > 1)
                AND name =:name
            #end
        ]]>
    </query>

 在系统加载时，需要把配置文件加载到系统中。加载代码关键部分如下：

package com.zuidaima.util
public class DynamicHibernateImpl implements InitializingBean, ResourceLoaderAware, ApplicationContextAware{
        public void afterPropertiesSet() throws Exception {
           for (int i = 0; i < fileNames.size(); i++) {
              String fileName = ((String) fileNames.get(i)).trim();
              if (resourceLoader instanceof ResourcePatternResolver) {                
                try {
                     Resource[] resources=         ((ResourcePatternResolver) resourceLoader).getResources(fileName);
                    buildHQLMap(resources);
                  } catch (IOException ex) {
                     throw new Exception("Could not resolve sql definition resource pattern ["                     + fileName + "]", ex);
                 }
             } else {               
                 Resource resource = resourceLoader.getResource(fileName);
                 buildHQLMap(new Resource[] { resource });
             }
         }
     }
  protected void buildHQLMap(Resource[] resources) throws Exception {
         for (int i = 0; i < resources.length; i++) {
             buildHQLMap(resources[i]);
         }
     }
  private void buildHQLMap(Resource resource) throws Exception {
         try {
             InputSource inputSource = new InputSource(resource.getInputStream());
             org.w3c.dom.Document doc = this.documentLoader.loadDocument(inputSource, null, null, org.springframework.util.xml.XmlValidationModeDetector.VALIDATION_NONE, false);
             Element root = doc.getDocumentElement();
             List<Element> querys = DomUtils.getChildElements(root);
             for(Element query:querys){
                 String queryName = query.getAttribute("name");
                 if (StringUtils.isEmpty(queryName)) {
                     throw new Exception("DynamicHibernate Service : name is essential attribute in a <query>.");
                 }
                 if(statements.containsKey(queryName)){
                     throw new Exception("DynamicHibernate Service : duplicated query in a <query>."+queryName);
                 }
                 statements.put(queryName, DomUtils.getTextValue(query));
             }
         } catch (SAXParseException se) {
             throw se;
         } catch (IOException ioe) {
             throw ioe;
         }
     }