Spring JPA自定义实现（孔乙己的茴香豆）

[SherryLang]

主要目的

获取EntityManager的实例，使用实例的方法来实现creatQuery

第一种实现：最原始的方式

package com.xxxxx.repository.base.impl;

import java.io.Serializable;
import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.springframework.data.domain.Example;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;

import com.xxxxx.repository.base.BasicRepository;
import com.xxxxx.support.GenericsTool;

/** 
 * 对外相当于simpleJpaRepository的功能
 * implements BasicRepository<T, ID>的部分可以不要，并且去掉@Override注解，相当于JPA的方法全部使用em自定义实现
*/
public class BasicDAO<T, ID extends Serializable> implements BasicRepository<T, ID>{

	@PersistenceContext
	protected EntityManager entityManager;

	private BasicRepository<T, ID> basicRepository;

	@SuppressWarnings("unchecked")
	private BasicRepository<T, ID> getBasicRepository() {
		if (null == basicRepository) {
			//通过反射，Class声明的范型参数的类型，用于实例化BasicRepositoryImpl对象，效果同Factory 
			basicRepository = new BasicRepositoryImpl<T, ID>(
					(Class<T>) GenericsTool.getSuperClassGenricType(getClass()), entityManager);
		}
		return basicRepository;
	}

 	@Override
	public List<T> findAll() {
		return getBasicRepository().findAll();
	}
	
	@Override
        // ...(父类的方法全部Override一遍)

}

其中用到的工具类方法如下：

package com.xxxxx.constant;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 反射转换对象什么的泛型参数类型
 */
public class GenericsTool {
	
	private static final Logger log = LoggerFactory.getLogger(GenericsTool.class);
	
	/**
	 * 通过反射,获得定义Class时声明的父类的范型参数的类型
	 * @param clazz 类对象
	 * @return 泛型类型
	 */
	public static Class<?> getSuperClassGenricType(Class<?> clazz) {
		return getSuperClassGenricType(clazz, 0);
	}
	
	/**
	 * 通过反射,获得定义Class时声明的父类的范型参数的类型
	 * @param clazz 类对象
	 * @param index 泛型位置，从0开始
	 * @return 泛型类型
	 */
	public static Class<?> getSuperClassGenricType(Class<?> clazz, int index) {
		Type genType = clazz.getGenericSuperclass();
		if (!(genType instanceof ParameterizedType)) {
			log.warn(clazz.getSimpleName() + "'s superclass not ParameterizedType");
			return Object.class;
		}
		Type[] params = ((ParameterizedType)genType).getActualTypeArguments();
		if (index >= params.length || index < 0) {
			log.warn("Index: " + index + ", Size of " + clazz.getSimpleName() + "'s Parameterized Type: " + params.length);
			return Object.class;
		}
		if (!(params[index] instanceof Class<?>)) {
			log.warn(clazz.getSimpleName() + " not set the actual class on superclass generic parameter");
			return Object.class;
		}
		return (Class<?>)params[index];
	}
}

第二种实现：Factory构造Bean，然而在接口中暴露了函数体

6月9日白天的代码
《深入实践Spring Boot》P83：自定义的接口必须在程序启动时装配，才能正常使用……

第三种实现：实现CccPageRepository接口，避免使用default修饰

CccPageRepository 接口继承自JpaRepository，只要需要定义方法名（避免暴露函数体），并且使用@NoRepositoryBean注解：

package com.xxxx.repository;

import java.util.List;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.repository.NoRepositoryBean;

import com.xxxx.domain.CccPage;
@NoRepositoryBean
public interface CccPageRepository extends JpaRepository<CccPage, Long>{
	List<CccPage> findByDocNo(String docNo);
	List<CccPage> searchCccByKeyword(String fieldName, String[] keywords);
}

实现类内部定义私有的EntityManager实体，并且用@Autowired注入，用构造函数构造自身（包括父类）：

package com.xxxx.repository;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.Query;

import org.apache.commons.lang3.StringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.jpa.repository.support.SimpleJpaRepository;
import org.springframework.stereotype.Repository;

import com.xxxx.domain.CccPage;

@Repository
public class CccPageRepositoryImpl extends SimpleJpaRepository<CccPage, Long> implements CccPageRepository {

	private String[] fields = { "model", "productName", "docNo", "remarks" };
        
        //私有成员变量em
	private EntityManager em;
	 
	@Autowired
	public CccPageRepositoryImpl (EntityManager em) {
		super(CccPage.class, em);
		this.em = em;
	}

	@SuppressWarnings("unchecked")
	public List<CccPage> findByDocNo(String docNo) {
		Query query = em.createQuery("from CccPage where docNo=:docNo");
		query.setParameter("docNo", docNo);
		return query.getResultList();
	}

	@SuppressWarnings("unchecked")
	public List<CccPage> searchCccByKeyword(String fieldName, String[] keywords) {
		StringBuilder sqlString = new StringBuilder("");
		//隐藏函数体，主要功能是构造自定义的sqlString
		System.out.println(sqlString.toString());

		Query query = em.createQuery(sqlString.toString());
		List<CccPage> res = query.getResultList();
		return res;
	}

}

第四种实现：反射获取em实例

关键：基类BasicDAO 反射获取EntityManager实例

package com.xxxx.repository.base;

import java.lang.reflect.Field;

import javax.persistence.EntityManager;

import org.slf4j.LoggerFactory;
import org.springframework.data.jpa.repository.support.SimpleJpaRepository;

public interface BasicDAO {
	/**
	 * 通过SimpleJpaRepository的em属性，反射获取EntityManager的实例
	 * 
	 * @return
	 */
	default EntityManager getEntityManager() {
		try {
			Field f = SimpleJpaRepository.class.getDeclaredField("em");
			f.setAccessible(true);
			return (EntityManager) f.get(this);
		} catch (NoSuchFieldException | SecurityException | IllegalArgumentException | IllegalAccessException e) {
			LoggerFactory.getLogger(BasicDAO.class)
					.error("not get current entityManager from reflect SimpleJpaRepository's field", e);
		}
		return null;
	}
}

CccPageRepository 继承JpaRepository和基类BasicDAO

package com.xxxx.repository;

import java.util.List;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.repository.NoRepositoryBean;

import com.xxxx.domain.CccPage;
import com.xxxx.repository.base.BasicDAO;

/* 注意这里要继承BasicDAO！*/
@NoRepositoryBean
public interface CccPageRepository extends JpaRepository<CccPage, Long>, BasicDAO {

	List<CccPage> findByDocNo(String docNo);

	List<CccPage> searchCccByKeyword(String fieldName, String[] keywords);
}

实现类CccPageRepositoryImpl

package com.xxxx.repository;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.Query;

import org.apache.commons.lang3.StringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.jpa.repository.support.SimpleJpaRepository;
import org.springframework.stereotype.Repository;

import com.xxxx.domain.CccPage;

@Repository
public class CccPageRepositoryImpl extends SimpleJpaRepository<CccPage, Long> implements CccPageRepository {

	private String[] fields = { "model", "productName", "docNo", "remarks" };

	/*
	 * private EntityManager em;
	 */
	public CccPageRepositoryImpl (EntityManager em) {
		super(CccPage.class, em);
	}

	@SuppressWarnings("unchecked")
	public List<CccPage> findByDocNo(String docNo) {
		Query query = getEntityManager().createQuery("from CccPage where docNo=:docNo");
		query.setParameter("docNo", docNo);
		return query.getResultList();
	}

	@SuppressWarnings("unchecked")
	public List<CccPage> searchCccByKeyword(String fieldName, String[] keywords) {
		StringBuilder sqlString = new StringBuilder("");
		//隐藏函数体，主要功能是构造自定义的sqlString
		System.out.println(sqlString.toString());

		Query query = getEntityManager().createQuery(sqlString.toString());
		List<CccPage> res = query.getResultList();
		return res;
	}
}