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。
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。
Sq-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 users_table Where 1=1
#if($name && $name.length() > 1)
AND name =:name
#end
]]>
</query>
<query name="selectUserHQL">
<![CDATA[
FROM users
Where 1=1
#if($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：
1 public class DynamicHibernateImpl implements InitializingBean, ResourceLoaderAware, ApplicationContextAware
afterPropertiesSet()
throws Exception {
3 for (
int i = 0; i < fileNames.size(); i++) {
4 String fileName = ((String) fileNames.get(i)).trim();
5 if (resourceLoader
instanceof ResourcePatternResolver) {
6 try {
7 Resource[] resources=((ResourcePatternResolver) resourceLoader).getResources(fileName);
8 buildHQLMap(resources);
9 }
catch (IOException ex) {
10 throw new Exception("Could not resolve sql definition resource pattern [" + fileName + "]", ex);
11 }
12 }
else {
13 Resource resource = resourceLoader.getResource(fileName);
14 buildHQLMap(
new Resource[] { resource });
15 }
16 }
17 }
18 protected void buildHQLMap(Resource[] resources)
throws Exception {
19 for (
int i = 0; i < resources.length; i++) {
20 buildHQLMap(resources[i]);
21 }
22 }
23 private void buildHQLMap(Resource resource)
throws Exception {
24 try {
25 InputSource inputSource =
new InputSource(resource.getInputStream());
26 org.w3c.dom.Document doc =
this.documentLoader.loadDocument(inputSource,
null,
null, org.springframework.util.xml.XmlValidationModeDetector.VALIDATION_NONE,
false);
27 Element root = doc.getDocumentElement();
28 List<Element> querys = DomUtils.getChildElements(root);
29 for(Element query:querys){
30 String queryName = query.getAttribute("name");
31 if (StringUtils.isEmpty(queryName)) {
32 throw new Exception("DynamicHibernate Service : name is essential attribute in a <query>.");
33 }
34 if(statements.containsKey(queryName)){
35 throw new Exception("DynamicHibernate Service : duplicated query in a <query>."+queryName);
36 }
37 statements.put(queryName, DomUtils.getTextValue(query));
38 }
39 }
catch (SAXParseException se) {
40 throw se;
41 }
catch (IOException ioe) {
42 throw ioe;
43 }
44 }
Spring的配置文件示例如下：
<bean id="dynamicHibernate" class="com.company.DynamicHibernateImpl">
<property name="sessionFactory" ref="sessionFactory" />
<property name="simpleTemplate" ref="simpleTemplate" />
<property name="fileNames">
<list>
<value>classpath*:hibernate/dynamic/dynamic-hibernate-*.xml</value>
</list>
</property>
</bean>
下一步是在使用时调用sql并调用模板方法，进行sql动态化。
还是DynamicHibernateImpl这个类
1 public List findList(String queryName, Map params, int pageIndex, int pageSize) throws Exception {
2 Context context = generateVelocityContext(params);
3 Query query = findInternal(queryName, context);
4 if (pageIndex > 0 && pageSize > 0) {
5 query.setFirstResult((pageIndex - 1) * pageSize);
6 query.setMaxResults(pageSize);
7 }
8 return query.list();
9 };
10 private Context generateVelocityContext(Map<String, Object> params) {
11 VelocityContext context = new VelocityContext();
12 if (null == params) {
13 return null;
14 }
15 Iterator<String> iterator = params.keySet().iterator();
16 while (iterator.hasNext()) {
17 String key = iterator.next();
18 Object value = params.get(key);
19 if (null == value) {
20 continue;
21 }
22 context.put(key, value);
23 }
24 return context;
25 };
26 private Query findInternal(String queryName, Context context) throws Exception {
27 String sql = findSQLByVelocity(queryName, context);
28 Query query = sessionFactory.getCurrentSession().createQuery(sql);
29 String[] namedParams = query.getNamedParameters();
30 setProperties(query, context, namedParams);
31 return query;
32 };
33 private String findSQLByVelocity(String queryName, Context context) throws Exception {
34 if (context == null)
35 context = new VelocityContext();
36 String sql = getSqlByName(queryName);
37 StringWriter writer = new StringWriter();
38 Velocity.evaluate(context, writer, "Hibernate", sql);
39 sql = writer.toString();
40 return sql;
41 };
42 protected String getSqlByName(String queryKey) {
43 return statements.get(queryKey);
44 }
就这些。
大家也许有更好的方法，欢迎交流。
QQ:24889356