构建动态sql,其实说白了就是拼装sql语句,在这里我把传入的实体参数,属性有值的拼装进sql,为null的则忽略,要实现这个不用说,肯定要利用Java的反射功能。
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来看一个具有代表性的insert语句的构建:
/**
* 构建insert语句
*
* @param entity 实体映射对象
* @param nameHandler 名称转换处理器
* @return
*/
public static SqlContext buildInsertSql(Object entity, NameHandler nameHandler) {
Class<?> clazz = entity.getClass();
String tableName = nameHandler.getTableName(clazz.getSimpleName());
String primaryName = nameHandler.getPrimaryName(clazz.getSimpleName());
StringBuilder sql = new StringBuilder("insert into ");
List<Object> params = new ArrayList<Object>();
sql.append(tableName);
//获取属性信息
BeanInfo beanInfo = ClassUtils.getSelfBeanInfo(clazz);
PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();
sql.append("(");
StringBuilder args = new StringBuilder();
args.append("(");
for (PropertyDescriptor pd : pds) {
Object value = getReadMethodValue(pd.getReadMethod(), entity);
if (value == null) {
continue;
}
sql.append(nameHandler.getColumnName(pd.getName()));
args.append("?");
params.add(value);
sql.append(",");
args.append(",");
}
sql.deleteCharAt(sql.length() - 1);
args.deleteCharAt(args.length() - 1);
args.append(")");
sql.append(")");
sql.append(" values ");
sql.append(args);
return new SqlContext(sql, primaryName, params);
}
众所周知,Java的反射是性能较低的,也有性能较好的第三方实现如cglib,这里并没有使用。在我的实测中两者差距不大。
但是注意这里并没有使用属性的操作方式,也就是没有使用jdk反射获取属性的getDeclaredFields()方法,而是使用了BeanInfo和PropertyDescriptor,因为后者的运行效率要远远高于前者。
在我的实测中,构建一个拥有12个属性的JavaBean的动态sql,十万次所耗时间为900毫秒左右,完全可以接受。当然,这里对JavaBean的信息进行了缓存,如果不缓存时间将多耗上几个数量级。
下面顺便贴上完整的代码:
/**
* sql辅助为类
*
* User: liyd
* Date: 2/13/14
* Time: 10:03 AM
*/
public class SqlUtils {
/** 日志对象 */
private static final Logger LOG = LoggerFactory.getLogger(SqlUtils.class);
/**
* 构建insert语句
*
* @param entity 实体映射对象
* @param nameHandler 名称转换处理器
* @return
*/
public static SqlContext buildInsertSql(Object entity, NameHandler nameHandler) {
Class<?> clazz = entity.getClass();
String tableName = nameHandler.getTableName(clazz.getSimpleName());
String primaryName = nameHandler.getPrimaryName(clazz.getSimpleName());
StringBuilder sql = new StringBuilder("insert into ");
List<Object> params = new ArrayList<Object>();
sql.append(tableName);
//获取属性信息
BeanInfo beanInfo = ClassUtils.getSelfBeanInfo(clazz);
PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();
sql.append("(");
StringBuilder args = new StringBuilder();
args.append("(");
for (PropertyDescriptor pd : pds) {
Object value = getReadMethodValue(pd.getReadMethod(), entity);
if (value == null) {
continue;
}
sql.append(nameHandler.getColumnName(pd.getName()));
args.append("?");
params.add(value);
sql.append(",");
args.append(",");
}
sql.deleteCharAt(sql.length() - 1);
args.deleteCharAt(args.length() - 1);
args.append(")");
sql.append(")");
sql.append(" values ");
sql.append(args);
return new SqlContext(sql, primaryName, params);
}
/**
* 构建更新sql
*
* @param entity
* @param nameHandler
* @return
*/
public static SqlContext buildUpdateSql(Object entity, NameHandler nameHandler) {
Class<?> clazz = entity.getClass();
StringBuilder sql = new StringBuilder();
List<Object> params = new ArrayList<Object>();
String tableName = nameHandler.getTableName(clazz.getSimpleName());
String primaryName = nameHandler.getPrimaryName(clazz.getSimpleName());
//获取属性信息
BeanInfo beanInfo = ClassUtils.getSelfBeanInfo(clazz);
PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();
sql.append("update ");
sql.append(tableName);
sql.append(" set ");
Object primaryValue = null;
for (PropertyDescriptor pd : pds) {
Object value = getReadMethodValue(pd.getReadMethod(), entity);
if (value == null) {
continue;
}
String columnName = nameHandler.getColumnName(pd.getName());
if (primaryName.equalsIgnoreCase(columnName)) {
primaryValue = value;
}
sql.append(columnName);
sql.append(" = ");
sql.append("?");
params.add(value);
sql.append(",");
}
sql.deleteCharAt(sql.length() - 1);
sql.append(" where ");
sql.append(primaryName);
sql.append(" = ?");
params.add(primaryValue);
return new SqlContext(sql, primaryName, params);
}
/**
* 构建查询条件
*
* @param entity
* @param nameHandler
*/
public static SqlContext buildQueryCondition(Object entity, NameHandler nameHandler) {
//获取属性信息
BeanInfo beanInfo = ClassUtils.getSelfBeanInfo(entity.getClass());
// PropertyDescriptor[] pds = BeanUtils.getPropertyDescriptors(entityClass);
PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();
StringBuilder condition = new StringBuilder();
List<Object> params = new ArrayList<Object>();
int count = 0;
for (PropertyDescriptor pd : pds) {
Object value = getReadMethodValue(pd.getReadMethod(), entity);
if (value == null) {
continue;
}
if (count > 0) {
condition.append(" and ");
}
condition.append(nameHandler.getColumnName(pd.getName()));
condition.append(" = ?");
params.add(value);
count++;
}
return new SqlContext(condition, null, params);
}
/**
* 获取属性值
*
* @param readMethod
* @param entity
* @return
*/
private static Object getReadMethodValue(Method readMethod, Object entity) {
if (readMethod == null) {
return null;
}
try {
if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers())) {
readMethod.setAccessible(true);
}
return readMethod.invoke(entity);
} catch (Exception e) {
LOG.error("获取属性值失败", e);
throw new MincoderException(e);
}
}
}
获取BeanInfo时写了一个ClassUtils来实现,里面对Bean信息进行了缓存。因为项目使用spring,本来想使用spring提供的BeanUtils.getPropertyDescriptor()方法的,里面同样拥有缓存,但是该方法会把实体类父类的属性信息也获取出来,而PropertyDescriptor中又没法判断,这将直接导致拼装sql时字段的错误,因为你不知道哪些字段是操作当前表所需要的。没办法,查看jdk本身的Introspector类,发现里面有如下方法定义:
public static BeanInfo getBeanInfo(Class<?> beanClass, Class<?> stopClass) throws IntrospectionException
即可以指定在哪个类停止获取属性,这正是我们需要的,可惜spring没有进行封装,只能自己实现了,参考了spring的实现,使用WeakHashMap来防止内存的溢出,及时清空Introspector本身的缓存:
/**
* 类辅助
*
* User: liyd
* Date: 2/12/14
* Time: 10:08 PM
*/
public class ClassUtils {
/** 日志对象 */
private static final Logger LOG = LoggerFactory
.getLogger(ClassUtils.class);
/**
* Map keyed by class containing CachedIntrospectionResults.
* Needs to be a WeakHashMap with WeakReferences as values to allow
* for proper garbage collection in case of multiple class loaders.
*/
private static final Map<Class, BeanInfo> classCache = Collections
.synchronizedMap(new WeakHashMap<Class, BeanInfo>());
/**
* 获取类本身的BeanInfo,不包含父类属性
*
* @param clazz
* @return
*/
public static BeanInfo getSelfBeanInfo(Class<?> clazz) {
try {
BeanInfo beanInfo;
if (classCache.get(clazz) == null) {
beanInfo = Introspector.getBeanInfo(clazz, clazz.getSuperclass());
classCache.put(clazz, beanInfo);
// Immediately remove class from Introspector cache, to allow for proper
// garbage collection on class loader shutdown - we cache it here anyway,
// in a GC-friendly manner. In contrast to CachedIntrospectionResults,
// Introspector does not use WeakReferences as values of its WeakHashMap!
Class classToFlush = clazz;
do {
Introspector.flushFromCaches(classToFlush);
classToFlush = classToFlush.getSuperclass();
} while (classToFlush != null);
} else {
beanInfo = classCache.get(clazz);
}
return beanInfo;
} catch (IntrospectionException e) {
LOG.error("获取BeanInfo失败", e);
throw new MincoderException(e);
}
}
/**
* 初始化实例
*
* @param clazz
* @return
*/
public static Object newInstance(Class<?> clazz) {
try {
return clazz.newInstance();
} catch (Exception e) {
LOG.error("根据class创建实例失败", e);
throw new MincoderException(e);
}
}
}
另外创建了对象SqlContext来保存构建后的sql和参数信息,定义如下:
/**
* 执行sql的上下文内容
*
* User: liyd
* Date: 2/13/14
* Time: 10:40 AM
*/
public class SqlContext {
/** 执行的sql */
private StringBuilder sql;
/** 主键名称 */
private String primaryKey;
/** 参数,对应sql中的?号 */
private List<Object> params;
public SqlContext(StringBuilder sql, String primaryKey, List<Object> params) {
this.sql = sql;
this.primaryKey = primaryKey;
this.params = params;
}
//getter setter 略
}
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