Spring数据访问谋略

Spring数据访问策略
Spring封装的数据访问异常
与SQLException是一个Checked Exception不同，Spring定义的基本书籍访问异常DataAccessException是一个RuntimeException，DataAccessException继承自NestedRuntimeException，完整的保留了原始异常信息。

// HsqldbUtil类，创建Book表，并插入两条数据public static void startDatabase() { server = new Server(); server.setDatabaseName(0, "test"); server.setDatabasePath(0, "mem:bookstore"); server.setLogWriter(null); server.setErrWriter(null); server.start();}

<!-- 定义DataSource --><bean id="dataSource" value="org.hsqldb.jdbcDriver" /><property name="url" value="jdbc:hsqldb:mem:bookstore" /><property name="username" value="sa" /><property name="password" value="" /></bean><!-- 使用DriverManagerDataSource为了方便调试  实际中可方便更换为 --><bean id="dataSource" value="java:comp/env/jdbc/xxxDataSource"/></bean>

主键生成策略
1.数据库内置自增 （不好移植）
2.整形字段，程序控制主键自动增长 （集群时要严格控制同步）
3.UUID 根据计算机MAC地址和时间，随机计算生成，唯一 （128位整数，浪费空间）

public interface BookDao {    List<Book> queryAll();    List<Book> queryByAuthor(String author);    void create(Book book);    void update(Book book);    void delete(String id);}

JdbcTemplet

<!-- 注入dataSource --><bean id="jdbcTemplateBookDao" ref="dataSource" /></bean>

public class JdbcTemplateBookDao extends JdbcDaoSupport implements BookDao {    // ResultSet映射为Bean的方式    class BookRowMapper implements RowMapper {        public Object mapRow(ResultSet rs, int rowNum) throws SQLException {            Book book = new Book();            book.setId(rs.getString("id"));            book.setName(rs.getString("name"));            book.setAuthor(rs.getString("author"));            return book;        }    }    @SuppressWarnings("unchecked")    public List<Book> queryAll() {        return getJdbcTemplate().query(                "select * from Book",                new BookRowMapper());    }    @SuppressWarnings("unchecked")    public List<Book> queryByAuthor(String author) {        return getJdbcTemplate().query(                "select * from Book where author=?",                new Object[] { author },                new BookRowMapper());    }    public void create(Book book) {        getJdbcTemplate().update(                "insert into Book (id, name, author) values (?, ?, ?)",                new Object[] {book.getId(), book.getName(), book.getAuthor()});    }    public void update(Book book) {        getJdbcTemplate().update(                "update Book set name=?, author=? where id=?",                new Object[] {book.getName(), book.getAuthor(), book.getId()});    }    public void delete(String id) {        getJdbcTemplate().update(                "delete from Book where id=?",                new Object[] {id});    }}

集成Hibernate
Hibernate管理Java类到数据库表的映射，提供了强大的基于对象的查询语句HQL，大幅减少数据库访问需要编写的代码的SQL语句，通过“方言”，最大限度降低了对特定数据库的依赖。
Hibernate还提供了系列复杂功能来简化数据库操作。
1.延迟加载，不一次取得所有相关联的对象，而是希望访问某个对象是再去数据库读取
2.主动抓取，允许在一个查询操作中就获得所有关联的对象，减少数据库连接次数
3.缓存
4.级联操作，外键关联的表，更新一个表时，需要同时更新其他表，级联删除 级联更新

<bean id="sessionFactory"     ref="dataSource" /><property name="annotatedClasses"><list><value>example.chapter5.Book</value></list></property><property name="annotatedPackages"><list><value>example.chapter5</value></list></property><property name="hibernateProperties"><props><prop key="hibernate.dialect">org.hibernate.dialect.HSQLDialect</prop><prop key="hibernate.show_sql">true</prop><prop key="hibernate.jdbc.fetch_size">10</prop><prop key="hibernate.cache.provider_class">org.hibernate.cache.HashtableCacheProvider</prop></props></property><property name="eventListeners"><map><entry key="pre-update"><bean /></entry><entry key="pre-insert"><bean /></entry></map></property></bean>

@Entity(name="Book")public class Book {// @Entity 作为数据库表映射 @Id 主键  @Transient不需要持久化字段    private String id;    private String name;    private String author;    @Id    @Pattern(regex="[a-z0-9\\-]{36}", message="ID只能由英文字母,数字和-构成,长度为36个字符")    public String getId() { return id; }    public void setId(String id) { this.id = id; }    public String getName() { return name; }    public void setName(String name) { this.name = name; }    public String getAuthor() { return author; }    public void setAuthor(String author) { this.author = author; }}public class HibernateBookDao extends HibernateDaoSupport implements BookDao {    @SuppressWarnings("unchecked")    public List<Book> queryAll() {        return getHibernateTemplate().find("select b from Book as b");    }    @SuppressWarnings("unchecked")    public List<Book> queryByAuthor(String author) {        return getHibernateTemplate().find("select b from Book as b where b.author=?", author);    }    public void create(Book book) {        getHibernateTemplate().save(book);    }    public void delete(String id) {        Book book = (Book) getHibernateTemplate().load(Book.class, id);        getHibernateTemplate().delete(book);    }    public void update(Book book) {        getHibernateTemplate().update(book);    }}

集成Ibtais

<bean id="iBatisBookDao" value="ibatis-sql-map-config.xml" /><property name="dataSource" ref="dataSource" /></bean></property></bean>

public class IBatisBookDao extends SqlMapClientDaoSupport implements BookDao {    @SuppressWarnings("unchecked")    public List<Book> queryAll() {        return getSqlMapClientTemplate().queryForList("queryAll");    }    @SuppressWarnings("unchecked")    public List<Book> queryByAuthor(String author) {        return getSqlMapClientTemplate().queryForList("queryByAuthor", author);    }    public void create(Book book) {        getSqlMapClientTemplate().insert("create", book);    }    public void delete(String id) {        getSqlMapClientTemplate().delete("delete", id);    }    public void update(Book book) {        getSqlMapClientTemplate().update("update", book);    }}

集成JPA
Spring对JPA采用Adapter模式，使JPA和其他持久化机制（Hibernate Toplink JDO）拥有一致的编程模型。

<!--    LocalEntityManagerFactoryBean 提供了标准的JPA初始化配置  LocalContainerEntityManagerFactoryBean 更灵活，可以注入Spring管理的DataSource--><bean id="entityManagerFactory"     ref="dataSource"/><!-- Adapter 选择实现JPA的具体框架 --><property name="jpaVendorAdapter"><bean value="true" /><property name="generateDdl" value="false" /></bean></property></bean> <bean id="jpaTxManager" ref="entityManagerFactory" /></bean><tx:annotation-driven transaction-manager="jpaTxManager" />

public class JpaBookDao extends JpaDaoSupport implements BookDao {    @SuppressWarnings("unchecked")    public List<Book> queryAll() {        return getJpaTemplate().find("select b from Book b");    }    @SuppressWarnings("unchecked")    public List<Book> queryByAuthor(String author) {        return getJpaTemplate().find("select b from Book b where b.author=?", new Object[] { author });    }    public void create(Book book) {        getJpaTemplate().persist(book);    }    public void delete(String id) {        Book book = getJpaTemplate().find(Book.class, id);        getJpaTemplate().remove(book);    }    public void update(Book book) {        getJpaTemplate().merge(book);    }}

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