項(xiàng)目中使用Hibernate和JPA對(duì)數(shù)據(jù)庫(kù)對(duì)象進(jìn)行實(shí)例化，但是生成的方法不支持多條件查詢。而如果針對(duì)每一個(gè)數(shù)據(jù)庫(kù)對(duì)象進(jìn)行多條件查詢編碼，則會(huì)變得很麻煩，而且一旦以后發(fā)生表結(jié)構(gòu)發(fā)生變化，這些方法可能還需要進(jìn)行重新編碼。所以考慮編寫一個(gè)方法可以對(duì)數(shù)據(jù)庫(kù)對(duì)象進(jìn)行多條件查詢，并返回泛型對(duì)象，這樣就可以方便使用。具體實(shí)現(xiàn)思路如下：

第一步：編寫數(shù)據(jù)庫(kù)查詢參數(shù)對(duì)象，此部分包含兩個(gè)，一個(gè)是查詢實(shí)體名稱(QueryCondition.java)，一個(gè)是數(shù)據(jù)庫(kù)查詢條件對(duì)象(QueryParameter.java)。

數(shù)據(jù)庫(kù)查詢條件對(duì)象(QueryParameter.java)包含三個(gè)參數(shù)，分別為參數(shù)名、參數(shù)值、查詢條件表達(dá)式

package?com.imstudio.jpa;

public?class?QueryParameter?{

public?enum?QueryOperateType?{

Equal,?CharIn

}

public?String?ParameterName;

public?Object?ParameterValue;

public?QueryOperateType?ParameterType;

public?QueryParameter()?{

}

public?QueryParameter(String?parameterName,?Object?parameterValue,

QueryOperateType?parameterType)?{

this.ParameterName?=?parameterName;

this.ParameterValue?=?parameterValue;

this.ParameterType?=?parameterType;

}

public?String?getParameterName()?{

return?ParameterName;

}

public?QueryOperateType?getParameterType()?{

return?ParameterType;

}

public?Object?getParameterValue()?{

return?ParameterValue;

}

public?void?setParameterName(String?parameterName)?{

ParameterName?=?parameterName;

}

public?void?setParameterType(QueryOperateType?parameterType)?{

this.ParameterType?=?parameterType;

}

public?void?setParameterValue(Object?parameterValue)?{

ParameterValue?=?parameterValue;

}

}

查詢對(duì)象實(shí)體(QueryCondition.java)包含查詢實(shí)體名稱以及查詢參數(shù)對(duì)象

package?com.imstudio.jpa;

import?java.util.ArrayList;

import?java.util.List;

public?class?QueryCondition?{

public?String?ModelName;

public?List?Parameters?=?new?ArrayList();

public?QueryCondition()?{

}

public?QueryCondition(String?modelName)?{

this.ModelName?=?modelName;

}

public?QueryCondition(String?modelName,?List?parameters)?{

this.ModelName?=?modelName;

this.Parameters?=?parameters;

}

public?void?add(QueryParameter?queryParameter)?{

this.Parameters.add(queryParameter);

}

public?String?getModelName()?{

return?ModelName;

}

public?List?getParameters()?{

return?Parameters;

}

public?void?setModelName(String?modelName)?{

ModelName?=?modelName;

}

public?void?setParameters(List?parameters)?{

Parameters?=?parameters;

}

}

在完成上述兩個(gè)實(shí)體對(duì)象之后就可以具體查詢方法的編寫了，在查詢中使用到一個(gè)變量querySymbols，下述編碼是從配置文件web.xml中獲取，這里主要是為了在使用不同數(shù)據(jù)庫(kù)的時(shí)候查詢關(guān)鍵字標(biāo)示符的修改。同時(shí)為了增加查詢方法的通用性，查詢返回?cái)?shù)據(jù)這里定義為泛型。

package?com.imstudio.jpa;import?java.util.ArrayList;

import?java.util.List;

import?java.util.logging.Level;

import?javax.persistence.EntityManager;

import?javax.persistence.Query;

import?org.apache.struts2.ServletActionContext;

import?com.imstudio.jpa.QueryParameter.QueryOperateType;

public?class?QueryDataAction?{

public?String?errorCode;

public?QueryDataAction()?{

}

public?QueryDataAction(String?errorCode)?{

this.errorCode?=?errorCode;

}

public?String?getErrorCode()?{

return?errorCode;

};

@SuppressWarnings("unchecked")

public??List?queryByPropertys(QueryCondition?queryCondition)?{

String?querySymbols?=?ServletActionContext.getServletContext()

.getInitParameter("QuerySymbols");

StringBuffer?sqlBuffer?=?new?StringBuffer();

sqlBuffer.append("select?model?\n");

sqlBuffer.append("from?"?+?queryCondition.ModelName?+?"?as?model?\n");

boolean?first?=?true;

for?(int?pi?=?0;?pi?

if?(queryCondition.Parameters.get(pi).getParameterName()?!=?null)?{????????????????????????????????if?(first)?{

sqlBuffer.append("where?");

first?=?false;

}?else?{

sqlBuffer.append("and?");

}

if?(queryCondition.Parameters.get(pi).getParameterType()?==?QueryOperateType.Equal)?{

sqlBuffer.append("model."

+?queryCondition.Parameters.get(pi)

.getParameterName()????????????????????????????+?"?=?"

+?querySymbols????????????????????????????+?queryCondition.Parameters.get(pi)

.getParameterName()?+?"?\n");

}?else?if?(queryCondition.Parameters.get(pi).getParameterType()?==?QueryOperateType.CharIn)?{

sqlBuffer.append("InStr(model."

+?queryCondition.Parameters.get(pi)

.getParameterName()????????????????????????????+?"?,?"

+?querySymbols????????????????????????????+?queryCondition.Parameters.get(pi)

.getParameterName()?+?"?)?>?0?\n");

}

}

}

List?list?=?new?ArrayList();

try?{

EntityManagerHelper.log(sqlBuffer.toString(),?Level.INFO,?null);

EntityManager?emEntityManager?=?EntityManagerHelper

.getEntityManager();

Query?queryObject?=?emEntityManager.createQuery(sqlBuffer

.toString());

for?(int?li?=?0;?li?

queryObject.setParameter(queryCondition.Parameters.get(li)

.getParameterName(),?queryCondition.Parameters.get(li)

.getParameterValue());

}

list?=?queryObject.getResultList();

emEntityManager.close();

}?catch?(RuntimeException?re)?{

errorCode?+=?"CM000006";

EntityManagerHelper.log("queryByPropertys?error",?Level.SEVERE,?re);

throw?re;

}????????return?list;

}

public?void?setErrorCode(String?errorCode)?{

this.errorCode?=?errorCode;

}

}

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