JPA利用Java反射机制动态构建sql
第一步：在项目pom.xml 加入 JPA 框架的 maven 依赖坐标
<!-- 数据库 ORM 框架 -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
第二步：在项目中的 model 层下创建一个实体类 CityData
/** * @author chaoyou * @email * @date 2019-10-8 17:55 * @Description 城市信息实体类 */ @Entity @Table(name = "city_data") public class CityData implements Serializable { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @Column(unique = true) private String cityCode; // 城市编码 @Column(unique = true) private String cityName; // 城市名字 @Column private String area; // 区域 @Column private String province; // 省份/直辖市 @Column private String prefectureLevel; // 地级城市 @Column private String town; // 县城 @Column private Integer level; // 城市等级：1、省会城市，2、地级城市，3、直辖市，4、县级市 @Column(name = "create_time", updatable = false) @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8") private Date createTime; // 创建时间 @Column(name = "update_time", insertable = false) @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8") private Date updateTime; // 更新时间 @Column private String cityRank; //城市级别 （T1，T2） public CityData() { } public CityData(Long id) { this.id = id; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getCityCode() { return cityCode; } public void setCityCode(String cityCode) { this.cityCode = cityCode; } public String getCityName() { return cityName; } public void setCityName(String cityName) { this.cityName = cityName; } public String getArea() { return area; } public void setArea(String area) { this.area = area; } public String getProvince() { return province; } public void setProvince(String province) { this.province = province; } public String getPrefectureLevel() { return prefectureLevel; } public void setPrefectureLevel(String prefectureLevel) { this.prefectureLevel = prefectureLevel; } public String getTown() { return town; } public void setTown(String town) { this.town = town; } public Integer getLevel() { return level; } public void setLevel(Integer level) { this.level = level; } public Date getCreateTime() { return createTime; } public void setCreateTime(Date createTime) { this.createTime = createTime; } public Date getUpdateTime() { return updateTime; } public void setUpdateTime(Date updateTime) { this.updateTime = updateTime; } public String getCityRank() { return cityRank; } public void setCityRank(String cityRank) { this.cityRank = cityRank; } }
第三步：在项目的 dao 层下创建一个供外部调用的接口 EntryMapper
import java.lang.reflect.Field; import java.util.List; /** * @author chaoyou * @email * @date 2020-6-11 14:56 * @Description 定义接口用于 获取实体 */ public interface EntryMapper { /** * 获取实体类对应数据表的表名 */ String getEntryTableName(Class<?> clazz); /** * 获取实体类对应数据表的主键字段 */ String getPKFieldName(Class<?> clazz); /** * 获取实体类对应数据表的外键字段 */ List<String> getFKFieldName(Class<?> clazz); /** * 获取实体类对应数据表的所有字段列名 */ List<String> getSequenceName(Class<?> clazz); /** * 获取实体类对应数据表的所有变量 */ List<Field> getFieldList(Class<?> clazz); /** * 获取实体类对应数据表的常规插入操作的 sql 语句 */ String getSqlToSave(Class<?> clazz); /** * 获取实体类对应数据表的常规更新操作的 sql 语句 */ String getSqlToUpdate(Class<?> clazz, String field); }
第四步：在项目的 impl 层下创建一个对 EntryMapper 接口的实现类
import org.apache.commons.lang3.StringUtils; import org.springframework.stereotype.Component; import org.springframework.util.Assert; import javax.persistence.*; import java.lang.reflect.Field; import java.util.ArrayList; import java.util.List; /** * @author chaoyou * @email * @date 2020-6-11 14:47 * @Description 这是获取实体类型信息的工具类 */ @Component public class JpaEntryMapper implements EntryMapper { /** * 获取实体类的名字 * * @param clazz 实体对象 * @return */ @Override public String getEntryTableName(Class<?> clazz) { // 校验参数对象是否为空 Assert.notNull(clazz, "clazz不能为空"); // 获取「Table」注解的控制权 Table tableAnno = clazz.getAnnotation(Table.class); // 校验是否有「table」注解 Assert.notNull(tableAnno, "@Table注解未设置"); // 检验「table」注解是否设置 name 属性值 Assert.state(StringUtils.isNotEmpty(tableAnno.name()), "@Table 的 name 属性未设置"); return tableAnno.name(); } /** * 获取实体类中的主键属性名 * * @param clazz 实体对象 * @return */ @Override public String getPKFieldName(Class<?> clazz) { Assert.notNull(clazz, "clazz不能为空"); // 通过「Java反射机制」拿到实体类的所有被 private 修饰的属性(不包括继承属性) Field[] fields = clazz.getDeclaredFields(); // 获取参数类中所有public的属性，包括继承的public属性 // Field[] fields = clazz.getFields(); String pk = null; if (fields.length == 0){ return pk; } /** * 遍历属性列表，找到被「@Id」注解修饰的属性 */ for (Field field : fields){ if (field.getAnnotation(Id.class) != null){ pk = field.getName(); break; } } return pk; } /** * 获取实体类中的外键属性 * * @param clazz * @return */ @Override public List<String> getFKFieldName(Class<?> clazz) { Assert.notNull(clazz, "clazz不能为空"); List<String> fks = new ArrayList<>(); String fk = null; Field[] fields = clazz.getDeclaredFields(); if (fields.length == 0){ return fks; } /** * 遍历属性列表，找到被「JoinColumn」注解修饰的属性 */ for (Field field : fields){ JoinColumn joinColumn = field.getAnnotation(JoinColumn.class); if (joinColumn != null){ if (!"".equals(joinColumn.name()) && !"".equals(joinColumn.referencedColumnName())){ fks.add(joinColumn.name() + "-" + joinColumn.referencedColumnName() + "-" + field.getName()); } else if (!"".equals(joinColumn.name()) && "".equals(joinColumn.referencedColumnName())){ fks.add(joinColumn.name() + "-id" + "-" + field.getName()); } else if ("".equals(joinColumn.name()) && !"".equals(joinColumn.referencedColumnName())){ fks.add(field.getName() + "-" + joinColumn.referencedColumnName() + "-" + field.getName()); } else if ("".equals(joinColumn.name()) && "".equals(joinColumn.referencedColumnName())){ fks.add(field.getName() + "-id" + "-" + field.getName()); } break; } } return fks; } /** * 获取实体类中所有属性对应的持久化字段(主键除外) * * @param clazz * @return */ @Override public List<String> getSequenceName(Class<?> clazz) { Assert.notNull(clazz, "clazz不能为空"); List<String> fieldList = null; Field[] fields = clazz.getDeclaredFields(); if (fields.length == 0){ return fieldList; } fieldList = new ArrayList<>(); // 普通持久化字段 Column column = null; // 非持久化字段 Transient tran = null; // 外键字段 JoinColumn joinColumn = null; for (Field field : fields){ tran = field.getAnnotation(Transient.class); if (tran != null){ continue; } column = field.getAnnotation(Column.class); joinColumn = field.getAnnotation(JoinColumn.class); if (column != null){ if (!"".equals(column.name())){ // Column 注解的 name 属性作为其对应的数据表映射字段 fieldList.add(column.name()); } else{ fieldList.add(field.getName()); } } else if (joinColumn != null){ if (!"".equals(joinColumn.name())){ // JoinColumn 注解的 name 属性作为其对应的数据表映射字段 fieldList.add(joinColumn.name()); } else{ fieldList.add(field.getName()); } } } return fieldList; } /** * 获取实体类中所有持久化字段的属性 * * @param clazz * @return */ @Override public List<Field> getFieldList(Class<?> clazz) { Assert.notNull(clazz, "clazz不能为空"); List<Field> fieldList = null; Field[] fields = clazz.getDeclaredFields(); if (fields.length == 0){ return fieldList; } fieldList = new ArrayList<>(); Column column = null; // 非持久化字段注解 Transient tran = null; JoinColumn joinColumn = null; for (Field field : fields){ tran = field.getAnnotation(Transient.class); if (tran != null){ continue; } column = field.getAnnotation(Column.class); joinColumn = field.getAnnotation(JoinColumn.class); if (column != null || joinColumn != null){ fieldList.add(field); } } return fieldList; } /** * 设置一个该实体类的 insert 持久化 sql * * @param clazz * @return */ @Override public String getSqlToSave(Class<?> clazz) { List<String> list = getSequenceName(clazz); List<String> sqls = new ArrayList<>(); for (int i=0; i<list.size(); i++){ sqls.add("?"); } String sql = "insert into " + getEntryTableName(clazz) + "(" + ArrayUtil.getStringByArray(list.toArray(), ", ") + ") values(" + ArrayUtil.getStringByArray(sqls.toArray(), ", ") + ")"; return sql; } /** * 设置一个该实体类的 update 持久化 sql * * @param clazz * @param field * @return */ @Override public String getSqlToUpdate(Class<?> clazz, String field) { List<String> list = getSequenceName(clazz); List<String> sqls = new ArrayList<>(); for (int i=0; i<list.size(); i++){ sqls.add(list.get(i) + "=?"); } String sql = "update " + getEntryTableName(clazz) + " set " + ArrayUtil.getStringByArray(sqls.toArray(), ", ") + " where " + field + "=?"; return sql; } }
第五步：在 test 层下创建一个测试类LCYTest
import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.test.context.SpringBootTest; import org.springframework.test.context.ActiveProfiles; import org.springframework.test.context.junit4.SpringRunner; import java.lang.reflect.Field; import java.text.ParseException; import java.util.Date; import java.util.List; /** * @author chaoyou * @email * @date 2020-8-12 16:44 * @Description * @Reference */ @RunWith(SpringRunner.class) @SpringBootTest public class LCYTest { @Autowired private EntryMapper entryMapper; @Test public void test09(){ String entryTableName = entryMapper.getEntryTableName(CityData.class); String pkFieldName = entryMapper.getPKFieldName(CityData.class); List<String> fkFieldNameList = entryMapper.getFKFieldName(CityData.class); List<String> sequenceNameList = entryMapper.getSequenceName(CityData.class); List<Field> fieldList = entryMapper.getFieldList(CityData.class); String sqlToSave = entryMapper.getSqlToSave(CityData.class); String sqlToUpdate = entryMapper.getSqlToUpdate(CityData.class, "id"); System.out.println("entryTableName：" + entryTableName); System.out.println("pkFieldName：" + pkFieldName); System.out.println("fkFieldNameList：" + fkFieldNameList); System.out.println("sequenceNameList：" + sequenceNameList); System.out.println("sqlToSave：" + sqlToSave); System.out.println("sqlToUpdate：" + sqlToUpdate); } }
第六步：当然就是看结果了
