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]);
else
se.setOutputFile("create_table.sql");
else
se.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 "";
}