让Hibernate生成的DDL脚本自动增加注释
我们知道可以通过Hibernate对象自动生成DDL建表语句，通过PowerDesigner工具可以反向工程生成数据字典，但是在生成的DDL中一直不能写上中文的注释，这就使我们生成的数据字典不具有可用性。
这个假期宅在家里调试代码，发现Hibernate的Dialect,Table,Column的映射中已经做了comment的处理，只是Hibernate团队认为这个功能的重要性太小，一直没有时间提供这个需求，于是就自己动手实现这个功能了，这可是使用我们的数据对象代码与数据字典文档同步的关键一环啊！
通过对Hibernate代码的跟踪发现了处理映射的逻辑是在代码AnnotationBinder中，我们不需要在运行期间处理comment，只是在用SchemaExport时处理就可以，于是简单的实现了此功能：
1. 增加一个注解 @Comment("这是表的说明，也可以是字段的说明")，适用在类名和属性名
2. 复制org.hibernate.cfg.AnnotationBuilder代码为org.hibernate.cfg.MyAnnotationBuilder，处理注解@Comment
3. 复制org.hibernate.cfg.Configuration为org.hibernate.cfg.MyConfiguration，将AnnotationBuilder的调用换成MyAnnotationBuilder
3. 实现SchemaExportTool类，传入MyConfiguration处理Hibernate对象的映射关系，并生成DDL
以上思路在基于Hibernate 4.2.3版本在MySql 5.1上测试成功，因为代码只是在开发期运行，不需要良好的结构和优化，所以只是简单实现了，需要此功能的朋友可以自己实现。
以下是处理结果示例：
@Entity@Table(name = "AuditRecord_")@Comment("系统审计表")@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)public class AuditRecord implements Serializable {private static final long serialVersionUID = 8844543936912679937L;@Id@GeneratedValue@Comment("ID主键")private Long id;@Comment("审计类型")@Column(length = 30)private String auditType;@Comment("操作人")@ManyToOne@JoinColumn(name = "userId")private Passport operator;// 操作简述@Comment("操作简述")@Column(length = 4000)private String description;@Comment("创建时间")private Date creationTime;}
生成的DDL如下：
create table audit_record_ ( id bigint not null auto_increment comment 'ID主键', audit_type varchar(30) comment '审计类型', creation_time datetime comment '创建时间', description longtext comment '操作简述', user_id bigint comment '操作人', primary key (id) ) comment='系统审计表';
主要代码片断如下：
import java.io.IOException;import java.util.Properties;import javax.persistence.Embeddable;import javax.persistence.Entity;import javax.persistence.MappedSuperclass;import org.hibernate.MappingException;import org.hibernate.cfg.MyConfiguration;import org.hibernate.tool.hbm2ddl.SchemaExport;import org.springframework.core.io.Resource;import org.springframework.core.io.support.PathMatchingResourcePatternResolver;import org.springframework.core.io.support.ResourcePatternResolver;import org.springframework.core.io.support.ResourcePatternUtils;import org.springframework.core.type.classreading.CachingMetadataReaderFactory;import org.springframework.core.type.classreading.MetadataReader;import org.springframework.core.type.classreading.MetadataReaderFactory;import org.springframework.core.type.filter.AnnotationTypeFilter;import org.springframework.core.type.filter.TypeFilter;import org.springframework.util.ClassUtils;public class SchemaExportTool extends MyConfiguration {private static final long serialVersionUID = 1L;private static final String RESOURCE_PATTERN = "/**/*.class";private static final String PACKAGE_INFO_SUFFIX = ".package-info";private static final TypeFilter[] ENTITY_TYPE_FILTERS = new TypeFilter[] {new AnnotationTypeFilter(Entity.class, false),new AnnotationTypeFilter(Embeddable.class, false),new AnnotationTypeFilter(MappedSuperclass.class, false) };private final ResourcePatternResolver resourcePatternResolver;public SchemaExportTool() {this.resourcePatternResolver = ResourcePatternUtils.getResourcePatternResolver(new PathMatchingResourcePatternResolver());}public static void main(String[] args) {try {Properties p = new Properties();p.setProperty("hibernate.dialect","org.hibernate.dialect.MySQLDialect");SchemaExportTool cfg = new SchemaExportTool();cfg.addProperties(p);cfg.setNamingStrategy(new ImprovedMyNamingStrategy());cfg.scanPackage("com.share.passport.domain","com.share.authority.domain", "com.share.utils.domain");SchemaExport se = new SchemaExport(cfg);if (null != args && args.length > 1)if ("-f".equals(args[0]))se.setOutputFile(args[1]);elsese.setOutputFile("create_table.sql");elsese.setOutputFile("create_table.sql");se.setDelimiter(";");// se.drop(false, false);se.create(false, false);} catch (Exception e) {e.printStackTrace();}}private SchemaExportTool scanPackage(String... packagesToScan) {try {for (String pkg : packagesToScan) {String pattern = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX+ ClassUtils.convertClassNameToResourcePath(pkg)+ RESOURCE_PATTERN;Resource[] resources = this.resourcePatternResolver.getResources(pattern);MetadataReaderFactory readerFactory = new CachingMetadataReaderFactory(this.resourcePatternResolver);for (Resource resource : resources) {if (resource.isReadable()) {MetadataReader reader = readerFactory.getMetadataReader(resource);String className = reader.getClassMetadata().getClassName();if (matchesEntityTypeFilter(reader, readerFactory)) {addAnnotatedClass(this.resourcePatternResolver.getClassLoader().loadClass(className));} else if (className.endsWith(PACKAGE_INFO_SUFFIX)) {addPackage(className.substring(0,className.length()- PACKAGE_INFO_SUFFIX.length()));}}}}return this;} catch (IOException ex) {throw new MappingException("Failed to scan classpath for unlisted classes", ex);} catch (ClassNotFoundException ex) {throw new MappingException("Failed to load annotated classes from classpath", ex);}}/** * Check whether any of the configured entity type filters matches the * current class descriptor contained in the metadata reader. */private boolean matchesEntityTypeFilter(MetadataReader reader,MetadataReaderFactory readerFactory) throws IOException {for (TypeFilter filter : ENTITY_TYPE_FILTERS) {if (filter.match(reader, readerFactory)) {return true;}}return false;}}/** * $Id:$ */package com.share.utils.hibernate;import org.hibernate.annotations.common.reflection.XClass;import org.hibernate.annotations.common.reflection.XProperty;import org.hibernate.cfg.Ejb3Column;import org.hibernate.mapping.PersistentClass;import com.share.annotations.Comment;public class CommentBinder { public static void bindTableComment(XClass clazzToProcess, PersistentClass persistentClass) { if (clazzToProcess.isAnnotationPresent(Comment.class)) { String tableComment = clazzToProcess.getAnnotation(Comment.class).value(); persistentClass.getTable().setComment(tableComment); } } public static void bindColumnComment(XProperty property, Ejb3Column[] columns) { if (null != columns) if (property.isAnnotationPresent(Comment.class)) { String comment = property.getAnnotation(Comment.class).value(); for (Ejb3Column column : columns) { column.getMappingColumn().setComment(comment); } } } public static void bindColumnComment(XProperty property, Ejb3Column column) { if (null != column) if (property.isAnnotationPresent(Comment.class)) { String comment = property.getAnnotation(Comment.class).value(); column.getMappingColumn().setComment(comment); } }}/** * $Id:$ */package com.share.annotations;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Target({ElementType.TYPE,ElementType.FIELD})@Retention(RetentionPolicy.RUNTIME)public @interface Comment { String value() default "";}