注解模拟数据库持久化框架

一、数据库持久化？

dao层的model一般会对应一个数据表，而model中的属性对应表中的字段。而在我们进行数据库的增删改查的时候，一般直接通过写SQL语句，填写增删改查字段来进行。如果我们能将model里面的属性与数据表的字段对应，将model与相应的表对应，然后注入到SQL语句中。当更改配置时，却不影响SQL的功能，不更改SQL语句。为了完成这一功能，通过注解实现最为合适。（在这里用到了JDBC、c3p0以及Spring）

二、实现过程

先看表的设计

在这里我们先给出相应的model
/* * 这里的model对应表mec_student_info,因为表的众多，所以给出接口的String类型常量 * 而下面的id数据表中对应学生的学号字段id * password对应为password * name为学生姓名name * peopleId对应数据表中的people_id(身份证号) * status为学生状态，对应status * 注意身份证号,model里面的peopleId对应数据表中的people_id * */@MecTable(table=IMecInfoTableName.STUDENT_INFO)public class StudentModel {@MecIDprivate String id;private String password;private String name;@MecField(field="people_id")private String peopleId;private String status;public StudentModel() {}public StudentModel(StudentModel student) {id = new String(student.id);password = new String(student.password);name = new String(student.name);peopleId = new String(student.peopleId);status = new String(student.status);}public String getId() {return id;}public void setId(String id) {this.id = id;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPeopleId() {return peopleId;}public void setPeopleId(String peopleId) {this.peopleId = peopleId;}public String getStatus() {return status;}public void setStatus(String status) {this.status = status;}@Overridepublic String toString() {return id + ":\npassword=" + password + "\nname=" + name + "\npeopleId=" + peopleId+ "\nstatus=" + status;}}

在这里我们可以发现，其中有了三个注解，MecField、MecId、MecTable，关于这三个注解，在下面的代码中给出详细解释

/* * 用于类，指明对应的是哪个表 * */@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.TYPE)public @interface MecTable {String table();}/* * ID作为主键比较特殊，专门给一个注解作为标识 * */@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface MecID {}/* * 这个注解用于标写对应的数据表的字段名称 * 它作用于model中的属性 * 如果model中的属性与数据表对应的字段相同，则不加此注解 * 如果不相同，添加此注解，参考model中的peopleId * */@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface MecField {String field();}

通过注解，我们将model中的属性与数据表中的字段对应了起来，而后面要做的，就是解析并且注入到SQL语句中

/* * 这个类可以说是上面studentModel里面属性的model * */public class FieldDefination {//属性的名字private String propertyName;//属性对应的表字段名字private String fieldName;//属性的Field类private Field property;//属性的类型private Class<?> propertyType;protected FieldDefination() {}/*此方法将从数据库获取到的数据反射进来，并且注入至相应属性*/public void setProperty(Object object, ResultSet resultSet) {property.setAccessible(true);try {String value = resultSet.getString(fieldName);if(value != null) {property.set(object, value);}} catch (SQLException e) {e.printStackTrace();} catch (IllegalArgumentException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();}}protected String getPropertyName() {return propertyName;}protected void setPropertyName(String propertyName) {this.propertyName = propertyName;}protected String getFieldName() {return fieldName;}protected void setFieldName(String fieldName) {this.fieldName = fieldName;}protected Field getProperty() {return property;}protected void setProperty(Field property) {this.property = property;}protected Class<?> getPropertyType() {return propertyType;}protected void setPropertyType(Class<?> propertyType) {this.propertyType = propertyType;}@Overridepublic String toString() {return "[" + propertyName + " - " + fieldName + "]"+ "\n成员:" + property+ "\n成员类型:" + propertyType;}}

下面进行注解的解析类的贴出

/* * 此类集中处理了注解的对应关系,并且对SQL语句进行了注入 * 关于此方法的内部实现，在这里不做详解，均为基本的java方法 * 但是关于mapRow()方法，我们在Record类中进行详解 * */public class RecordDefination <t> implements RowMapper<t> {//对应model的classprivate Class<?> klass;//model对应的表的名称private String table;//属性对应FieldDefinationprivate FieldDefination id;//装入一个map,键为field的name,值为属性对应的FieldDefinationprivate Map<string fielddefination=""> properties;//用于判断ID的唯一性private boolean done;protected RecordDefination(Class<?> klass) throws MultiIdException {done = false;if(!klass.isAnnotationPresent(MecTable.class)) {return;}this.klass = klass;MecTable mecTable = klass.getAnnotation(MecTable.class);this.table = mecTable.table();properties = new HashMap<>();Field[] fields = klass.getDeclaredFields();for(Field field : fields) {String fieldName = field.getName();FieldDefination fieldDefination = new FieldDefination();fieldDefination.setProperty(field);fieldDefination.setPropertyName(fieldName);fieldDefination.setPropertyType(field.getType());fieldDefination.setFieldName(fieldName);if(field.isAnnotationPresent(MecField.class)) {MecField mecField = field.getAnnotation(MecField.class);fieldDefination.setFieldName(mecField.field());}if(field.isAnnotationPresent(MecID.class)) {if(done == true) {throw new MultiIdException("关键字重复！");}done = true;id = fieldDefination;}properties.put(fieldName, fieldDefination);}}@SuppressWarnings("unchecked")@Overridepublic T mapRow(ResultSet resultSet, int count) throws SQLException {T object = null;try {object = (T) klass.newInstance();for(String property : properties.keySet()) {FieldDefination field = properties.get(property);field.setProperty(object, resultSet);}} catch (InstantiationException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();}return object;}protected String getBaseQuery() {StringBuffer stringBuffer = new StringBuffer("SELECT ");boolean firstField = true;for(String propertyName : properties.keySet()) {FieldDefination fieldDefination = properties.get(propertyName);if(!firstField) {stringBuffer.append(", ");}firstField = false;stringBuffer.append(fieldDefination.getFieldName());}stringBuffer.append(" FROM ");stringBuffer.append(table);return stringBuffer.toString();}protected String getQuery(Object id) {StringBuffer stringBuffer = new StringBuffer();stringBuffer.append(getBaseQuery());Class<?> idType = this.id.getPropertyType();stringBuffer.append(" WHERE ");stringBuffer.append(this.id.getFieldName());if(idType.equals(String.class)) {stringBuffer.append(" = '");stringBuffer.append(id.toString());stringBuffer.append("'");} else {stringBuffer.append(" = ");stringBuffer.append(id.toString());}return stringBuffer.toString();}}/*此类对RecordDefination进行了调用*/@Componentpublic class Record {@Autowiredprivate JdbcTemplate jdbc;/* * 此方法用于注入SQL语句，而调用的SQL语句，在RecordDefination里面，请参考 * 而jdbc.query(),返回了一个list，装有要取得的所有元素的信息 * */public <t> List<t> list(Class<?> klass) {try {RecordDefination<t> recordDefination = new RecordDefination<>(klass);return jdbc.query(new PreparedStatementCreator() {@Overridepublic PreparedStatement createPreparedStatement(Connection connection)throws SQLException {return connection.prepareStatement(recordDefination.getBaseQuery());}}, recordDefination);} catch (MultiIdException e) {e.printStackTrace();}return null;}/* * 此方法会取得相应学号对应的学生的信息 * 请百度<t> T org.springframework.jdbc.core.JdbcTemplate * .queryForObject(String sql, RowMapper<t> rowMapper) throws DataAccessException * 的使用 * */public <t> T get(Class<?> klass, Object id) {T object = null;try {RecordDefination<t> recordDefination = new RecordDefination<>(klass);String SQLString = recordDefination.getQuery(id);object = jdbc.queryForObject(SQLString, recordDefination);System.out.println(object);} catch (MultiIdException e) {e.printStackTrace();}return object;}}</string></t></t></t></t></t></t></t></t></t>

贴出test的代码

public class Test {public static void main(String[] args) {//下面语句仅仅是封装了Spring以及c3p0的启动MibernateBase.start();Record record;try {record = new SpringContextHolder().getBean(Record.class);record.get(StudentModel.class, "201604002006");System.out.println(record.list(StudentModel.class));} catch (SpringContextNotInitializedException e) {e.printStackTrace();}}}

至此，基本模拟了Hibnernate的增删改查功能，也就是模拟了所谓的transaction