Java 反射机制模拟hibernate实现持久化

转自：http://blog.youkuaiyun.com/ljjlzx/archive/2009/07/29/4390628.aspx

hibernate 可以使我们轻松的进行数据库的操作，
传递一个查询语句(类似 "select id,name from userInfo"),hibernate 会自动的将符合条件的
对象封装的list里面，供我们调用，大大简化了我们的代码量。下面就以一段代码模仿hibernate
的实现。

代码片段一(一般的查询方法)：
/** * 通用的查询方法 * 通过SQL语句,与传递进来的object * 将查询出来的sql结果,通过反射机制封装至object * 注: ojbect必须为POJO,或BEAN的类 * @param sql 查询SQL * @param objName 需要返回的列表内包含对象的类型 * @return 封装好的对象 */ public List getResult(String sql,String objName,int db_flag) throws Exception { PreparedStatement stmt = null; ResultSet rs = null; RecordReflection rr = null; //获得数据库的连接 dbConnection = new DbConn1().getDBConnection(); if(dbConnection != null) System.out.println("GetConn successful"); List result = null; try { stmt = dbConnection.prepareStatement(sql); rs = stmt.executeQuery(); if(rs != null){ System.out.println("GetRS successful"); } //具体内容见代码片段2 rr = new RecordReflection(); //通过传递 结果集 和 “对象的全名” 返回 对象列表,和 普通查询 这一步不同 result = rr.Relection(rs, objName); } catch (SQLException ex) { log.error("getResult is error:" + ex.getMessage()); ex.printStackTrace(); } finally { this.closeResultSet(rs); this.closeStatement(stmt); this.closeConnection(); } return result; //返回范类型集合,该集合中存储着符合条件的行与列 } 

代码片段二(RecordReflection 类)：
package com.ghrt.frame; import java.lang.reflect.Field; import java.lang.reflect.Method; import java.math.BigDecimal; import java.sql.ResultSet; import java.sql.ResultSetMetaData; import java.sql.Timestamp; import java.util.ArrayList; import java.util.Date; import java.util.Iterator; import java.util.List; import org.apache.log4j.Logger; public class RecordReflection { private Logger log = Logger.getLogger(RecordReflection.class); /** * 通过传递进来的ResultSet与对象名称,序列化为对象,塞入list * @param rs 结果集 * @param objName 对象 * @return list list里存储传递的objName的对象 */ public List Relection(ResultSet rs,String objName){ List list = null; try{ List resultList = this.ProcessResultSet(rs); list = this.ProcessObject(resultList, objName); }catch(Exception e){ log.error("Relection is error:" + e.getMessage()); } return list; } public List ProcessResultSet(ResultSet rs) throws PlatformException{ List listResult =new ArrayList(); int cols = 0; String colName=""; String colType=""; String colValue=""; try{ if(rs == null) //判断是否结果集为空,如果为空,直接返回 return null; LabelValue lv = null; //见代码片段3 List list = new ArrayList<LabelValue>(); ResultSetMetaData rsetMd = null; rsetMd = rs.getMetaData(); cols = rsetMd.getColumnCount(); while(rs.next()){ list = new ArrayList<LabelValue>(); for (int i=0;i<cols;i++){ colName = rsetMd.getColumnName(i+1); colType = rsetMd.getColumnTypeName(i+1); colValue = rs.getString(i+1); lv = new LabelValue(); lv.setName(colName); lv.setType(colType); lv.setValue(colValue); list.add(lv); } listResult.add(list); } }catch(Exception e){ log.error(" // Relection process ResultSet is error // " + e.getMessage()); throw new PlatformException("class RecordReflection ProcessResultSet is error: " + e.getMessage()); } return listResult; } public List ProcessObject(List list,String objName) throws PlatformException{ List resultList = null; try{ resultList = new ArrayList(); log.debug(" // list.size:" + list.size()); Iterator it = list.iterator(); while(it.hasNext()){//获取每条记录 List lvList = (List)it.next(); log.debug(" // lvList.size:" + lvList.size()); System.out.println("lvList:"+lvList.size()); Iterator lvIt = lvList.iterator(); Class clazz = Class.forName(objName); Object obj = clazz.newInstance(); while(lvIt.hasNext()){//获取记录里的每个字段 LabelValue lv = (LabelValue)lvIt.next(); //获取生成的object对象 Field[] fields = clazz.getDeclaredFields(); log.debug("// fileds.length // "+fields.length); // for(Field field:fields){ for(int i = 0;i<fields.length;i++){ Field field = fields[i]; System.out.println(fields[i]); log.debug("getname:"+field.getName()+" // lv.getName // "+lv.getName()); String fieldName = field.getName(); if(fieldName.equalsIgnoreCase(lv.getName())){ log.debug(" // fieldName//" + fieldName +" // fieldType //" + field.getType().getName()); log.debug(" // lv.getName // " + lv.getName() + " // lv.value // " + lv.getValue()); Method method = clazz.getDeclaredMethod( "set"+fieldName.substring(0,1).toUpperCase()+fieldName.substring(1) ,new Class[]{field.getType()}); if(field.getType().equals(String.class)){ //处理当为String类型情况 method.invoke(obj, new Object[]{this.toString(lv.getValue())}); }else if(field.getType().equals(Integer.class)){ //处理当为Integer类型情况 method.invoke(obj, new Object[]{this.toInteger(lv.getValue())}); }else if(field.getType().equals(Float.class)){ //处理当为Float类型情况 method.invoke(obj, new Object[]{this.toFloat(lv.getValue())}); }else if(field.getType().equals(Double.class)){ //处理当为Double类型情况 method.invoke(obj, new Object[]{this.toDouble(lv.getValue())}); }else if(field.getType().equals(BigDecimal.class)){ //处理当为BigDecimal类型情况 method.invoke(obj, new Object[]{this.toBigDecimal(lv.getValue())}); }else if(field.getType().equals(Long.class)){ //处理当为Long类型情况 method.invoke(obj, new Object[]{this.toLong(lv.getValue())}); }else if(field.getType().equals(Timestamp.class)){ //处理当为Timestamp类型情况 method.invoke(obj, new Object[]{this.toTimestamp(lv.getValue())}); }else if(field.getType().equals(int.class)){ //处理当为int类型情况 method.invoke(obj, new Object[]{this.toInteger(lv.getValue())}); }else if(field.getType().equals(float.class)){ //处理当为float类型情况 method.invoke(obj, new Object[]{this.toFloat(lv.getValue())}); }else if(field.getType().equals(double.class)){ //处理当为double类型情况 method.invoke(obj, new Object[]{this.toDouble(lv.getValue())}); }else if(field.getType().equals(Date.class)){ //处理当为Date类型情况 method.invoke(obj, new Object[]{this.toTimestamp(lv.getValue())}); }else if(field.getType().equals(short.class)){ //处理当为Short类型情况 log.debug(" // parse short // "); method.invoke(obj, new Object[]{this.toShort(lv.getValue())}); } } } } resultList.add(obj); } }catch(Exception ex){ log.error(" // process object is error // " + ex.getMessage()); throw new PlatformException("class RecordReflection ProcessObject is error: " + ex.getMessage()); } return resultList; } /** * 对Date类型转换 * @param args * @return */ public Date toDate(String args){ Date result = null; if(null == args || "".equals(args)) result = null; else try{ // result = BigDecimal.parseBigDecimal(args); result = new Date(args); }catch(Exception e){ result = null; log.error(" // RecordReflection parse Date is error // " + e.getMessage()); } return result; } /** * 对Timestamp类型转换 * @param args * @return */ public Timestamp toTimestamp(String args){ Timestamp result = null; if(null == args || "".equals(args)) result = null; else try{ // result = BigDecimal.parseBigDecimal(args); result = Timestamp.valueOf(args); }catch(Exception e){ result = null; log.error(" // RecordReflection parse Timestamp is error // " + e.getMessage()); } return result; } /** * 对BigDecimal类型转换 * @param args * @return */ public BigDecimal toBigDecimal(String args){ BigDecimal result = null; if(null == args || "".equals(args)) result = new BigDecimal(0); else try{ // result = BigDecimal.parseBigDecimal(args); result = new BigDecimal(args); }catch(Exception e){ result = new BigDecimal(0); log.error(" // RecordReflection parse BigDecimal is error // " + e.getMessage()); } return result; } /** * 对Long类型转换 * @param args * @return */ public Long toLong(String args){ Long result = null; if(null == args || "".equals(args)) result = new Long(0); else try{ result = Long.parseLong(args); }catch(Exception e){ result = new Long(0); log.error(" // RecordReflection parse Long is error // " + e.getMessage()); } return result; } /** * 对Double类型转换 * @param args * @return */ public Double toDouble(String args){ Double result = null; if(null == args || "".equals(args)) result = new Double(0); else try{ result = Double.parseDouble(args); }catch(Exception e){ result = new Double(0); log.error(" // RecordReflection parse Double is error // " + e.getMessage()); } return result; } /** * 对Float类型转换 * @param args * @return */ public Float toFloat(String args){ Float result = null; if(null == args || "".equals(args)) result = new Float(0); else try{ result = Float.parseFloat(args); }catch(Exception e){ result = new Float(0); log.error(" // RecordReflection parse Float is error // " + e.getMessage()); } return result; } /** * 对Integer类型转换 * @param args * @return */ public Integer toInteger(String args){ Integer result = null; if(null == args || "".equals(args)) result = 0; else{ try{ result = Integer.parseInt(args); }catch(Exception e){ result = 0; log.error(" // RecordReflection parse Integer is error // " + e.getMessage()); } } return result; } /** * 对Short类型转换 * @param args * @return */ public Short toShort(String args){ Short result = null; if(null == args || "".equals(args)) result = 0; else{ try{ result = Short.parseShort(args); }catch(Exception e){ result = 0; log.error(" // RecordReflection parse Short is error // " + e.getMessage()); } } return result; } /** * 重写了对String类型的转换 * @param args * @return */ public String toString(String args){ String result = null; if (null == args || "".equals(args)) result = ""; else result = args.toString(); return result; } } 

代码片段3(LabelValue 类):

package com.ghrt.frame; import java.io.Serializable; public class LabelValue implements Serializable{ private String name; private String value; private String type; private int id; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getValue() { return value; } public void setValue(String value) { this.value = value; } public String getType() { return type; } public void setType(String type) { this.type = type; } }