Spring 5 中文解析数据存储篇-JDBC数据存储(下)

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":5},"content":[{"type":"text","text":"3.7 作为Java对象JDBC操作模型"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"org.springframework.jdbc.object包包含一些类，这些类使你以更加面向对象的方式访问数据库。例如，你可以运行查询并将结果作为包含业务对象的列表返回，该业务对象的关联列数据映射到业务对象的属性。你还可以运行存储过程并运行update，delete和insert语句。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"许多Spring开发人员认为，下面描述的各种RDBMS操作类（StoredProcedure类除外）通常可以用直接的JdbcTemplate调用代替。通常，编写直接在JdbcTemplate上调用方法的DAO方法（与将查询封装为完整的类相对）更简单。但是，如果通过使用RDBMS操作类获得可测量的价值，则应继续使用这些类。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"###### 3.7.1 理解"},{"type":"codeinline","content":[{"type":"text","text":"SqlQuery"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"SqlQuery是可重用的、线程安全的类，它封装了SQL查询。子类必须实现newRowMapper(..)方法以提供RowMapper实例，该实例可以为遍历查询执行期间创建的ResultSet所获得的每一行创建一个对象。很少直接使用SqlQuery类，因为MappingSqlQuery子类为将行映射到Java类提供了更为方便的实现。扩展SqlQuery的其他实现是MappingSqlQueryWithParameters和UpdatableSqlQuery。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"###### 3.7.2 使用"},{"type":"codeinline","content":[{"type":"text","text":"MappingSqlQuery"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"MappingSqlQuery是可重用的查询，其中具体的子类必须实现抽象的mapRow(..)方法，以将提供的ResultSet的每一行转换为指定类型的对象。以下示例显示了一个自定义查询，该查询将t_actor关系中的数据映射到Actor类的实例："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"public class ActorMappingQuery extends MappingSqlQuery {\n\n public ActorMappingQuery(DataSource ds) {\n super(ds, \"select id, first_name, last_name from t_actor where id = ?\");\n declareParameter(new SqlParameter(\"id\", Types.INTEGER));\n compile();\n }\n\n @Override\n protected Actor mapRow(ResultSet rs, int rowNumber) throws SQLException {\n Actor actor = new Actor();\n actor.setId(rs.getLong(\"id\"));\n actor.setFirstName(rs.getString(\"first_name\"));\n actor.setLastName(rs.getString(\"last_name\"));\n return actor;\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"该类扩展了使用Actor类型参数化的MappingSqlQuery。此自定义查询的构造函数将DataSource作为唯一参数。在此构造函数中，可以使用DataSource和运行的SQL调用超类上的构造函数，以检索该查询的行。该SQL用于创建PreparedStatement，因此它可以包含在执行期间要传递的任何参数的占位符。你必须使用传入SqlParameter的declareParameter方法声明每个参数。SqlParameter具有名称，并且具有java.sql.Types中定义的JDBC类型。定义所有参数之后，可以调用compile()方法，以便可以准备并稍后执行。此类在编译后是线程安全的，因此，只要在初始化DAO时创建这些实例，就可以将它们保留为实例变量并可以重用。下面的示例演示如何定义此类："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"private ActorMappingQuery actorMappingQuery;\n\n@Autowired\npublic void setDataSource(DataSource dataSource) {\n this.actorMappingQuery = new ActorMappingQuery(dataSource);\n}\n\npublic Customer getCustomer(Long id) {\n return actorMappingQuery.findObject(id);\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"前面示例中的方法检索具有作为唯一参数传入的id的customer。由于只希望返回一个对象，因此我们以id为参数调用findObject便捷方法。相反，如果有一个查询返回一个对象列表并采用其他参数，则将使用其中一种执行方法，该方法采用以可以变参数形式传入的参数值数组。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"public List searchForActors(int age, String namePattern) {\n List actors = actorSearchMappingQuery.execute(age, namePattern);\n return actors;\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"###### 3.7.3 使用"},{"type":"codeinline","content":[{"type":"text","text":"SqlUpdate"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"SqlUpdate类封装了SQL更新。与查询一样，更新对象是可重用的，并且与所有RdbmsOperation类一样，更新可以具有参数并在SQL中定义。此类提供了许多类似于查询对象的execute(..)方法的update(..)方法。SQLUpdate类是具体的。可以将其子类化-例如，添加自定义更新方法。但是，你不必子类化SqlUpdate类，因为可以通过设置SQL和声明参数来轻松地对其进行参数化。以下示例创建一个名为execute的自定义更新方法："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"import java.sql.Types;\nimport javax.sql.DataSource;\nimport org.springframework.jdbc.core.SqlParameter;\nimport org.springframework.jdbc.object.SqlUpdate;\n\npublic class UpdateCreditRating extends SqlUpdate {\n\n public UpdateCreditRating(DataSource ds) {\n setDataSource(ds);\n setSql(\"update customer set credit_rating = ? where id = ?\");\n declareParameter(new SqlParameter(\"creditRating\", Types.NUMERIC));\n declareParameter(new SqlParameter(\"id\", Types.NUMERIC));\n compile();\n }\n\n /**\n * @param id for the Customer to be updated\n * @param rating the new value for credit rating\n * @return number of rows updated\n */\n public int execute(int id, int rating) {\n return update(rating, id);\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"###### 3.7.4 使用"},{"type":"codeinline","content":[{"type":"text","text":"StoredProcedure"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"StoredProcedure类是RDBMS存储过程的对象抽象的超类。此类是抽象的，并且其各种execute(..)方法均具有受保护的访问权限，除了通过提供更严格类型的子类之外，还可以防止使用。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"继承的sql属性是RDBMS中存储过程的名称。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"要为StoredProcedure类定义参数，可以使用SqlParameter或其子类之一。你必须在构造函数中指定参数名称和SQL类型，如以下代码片段所示："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"new SqlParameter(\"in_id\", Types.NUMERIC),\nnew SqlOutParameter(\"out_first_name\", Types.VARCHAR),"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"SQL类型是使用java.sql.Types常量指定的。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第一行（带有SqlParameter）声明一个IN参数。您可以将IN参数用于存储过程调用以及使用SqlQuery及其子类（"},{"type":"link","attrs":{"href":"https://docs.spring.io/spring/docs/5.2.8.RELEASE/spring-framework-reference/data-access.html#jdbc-SqlQuery","title":""},"content":[{"type":"text","text":"了解SqlQuery"}]},{"type":"text","text":"中介绍）的查询。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第二行（带有SqlOutParameter）声明将在存储过程调用中使用的out参数。还有一个用于InOut参数的SqlInOutParameter（为过程提供in值并返回值的参数）。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"对于in参数，除了名称和SQL类型外，还可以为数字数据指定精度，或者为自定义数据库类型指定类型名称。对于out参数，可以提供RowMapper来处理从REF游标返回的行的映射。另一个选择是指定一个SqlReturnType，它允许你定义返回值的自定义处理。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下一个简单DAO示例使用StoredProcedure调用任何Oracle数据库附带的函数(sysdate())。要使用存储过程功能，你必须创建一个扩展StoredProcedure的类。在此示例中，StoredProcedure类是一个内部类。但是，如果需要重用StoredProcedure，则可以将其声明为顶级类。此示例没有输入参数，但是使用SqlOutParameter类将输出参数声明为日期类型。execute()方法将运行该过程，并从结果Map中提取返回的日期。通过使用参数名称作为键，结果Map为每个声明的输出参数（在这种情况下只有一个）都有一个条目。以下清单显示了我们的自定义StoredProcedure类："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"import java.sql.Types;\nimport java.util.Date;\nimport java.util.HashMap;\nimport java.util.Map;\nimport javax.sql.DataSource;\nimport org.springframework.beans.factory.annotation.Autowired;\nimport org.springframework.jdbc.core.SqlOutParameter;\nimport org.springframework.jdbc.object.StoredProcedure;\n\npublic class StoredProcedureDao {\n\n private GetSysdateProcedure getSysdate;\n\n @Autowired\n public void init(DataSource dataSource) {\n this.getSysdate = new GetSysdateProcedure(dataSource);\n }\n\n public Date getSysdate() {\n return getSysdate.execute();\n }\n\n private class GetSysdateProcedure extends StoredProcedure {\n\n private static final String SQL = \"sysdate\";\n\n public GetSysdateProcedure(DataSource dataSource) {\n setDataSource(dataSource);\n setFunction(true);\n setSql(SQL);\n declareParameter(new SqlOutParameter(\"date\", Types.DATE));\n compile();\n }\n\n public Date execute() {\n // the 'sysdate' sproc has no input parameters, so an empty Map is supplied...\n Map results = execute(new HashMap());\n Date sysdate = (Date) results.get(\"date\");\n return sysdate;\n }\n }\n\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面的StoredProcedure示例包含两个输出参数（在本例中为Oracle REF游标）："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"import java.util.HashMap;\nimport java.util.Map;\nimport javax.sql.DataSource;\nimport oracle.jdbc.OracleTypes;\nimport org.springframework.jdbc.core.SqlOutParameter;\nimport org.springframework.jdbc.object.StoredProcedure;\n\npublic class TitlesAndGenresStoredProcedure extends StoredProcedure {\n\n private static final String SPROC_NAME = \"AllTitlesAndGenres\";\n\n public TitlesAndGenresStoredProcedure(DataSource dataSource) {\n super(dataSource, SPROC_NAME);\n declareParameter(new SqlOutParameter(\"titles\", OracleTypes.CURSOR, new TitleMapper()));\n declareParameter(new SqlOutParameter(\"genres\", OracleTypes.CURSOR, new GenreMapper()));\n compile();\n }\n\n public Map execute() {\n // again, this sproc has no input parameters, so an empty Map is supplied\n return super.execute(new HashMap());\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"请注意如何在TitlesAndGenresStoredProcedure构造函数中使用的clarifyParameter(..)方法的重载变体传递给RowMapper实现实例。这是重用现有功能的非常方便且强大的方法。接下来的两个示例提供了两个RowMapper实现的代码。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"TitleMapper类将提供的ResultSet中每一行的ResultSet映射到Title域对象，如下所示："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"import java.sql.ResultSet;\nimport java.sql.SQLException;\nimport com.foo.domain.Title;\nimport org.springframework.jdbc.core.RowMapper;\n\npublic final class TitleMapper implements RowMapper