Spring 5 中文解析數據存儲篇-JDBC數據存儲(下)

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":5},"content":[{"type":"text","text":"3.7 作爲Java對象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包包含一些類，這些類使你以更加面向對象的方式訪問數據庫。例如，你可以運行查詢並將結果作爲包含業務對象的列表返回，該業務對象的關聯列數據映射到業務對象的屬性。你還可以運行存儲過程並運行update，delete和insert語句。"}]},{"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":"許多Spring開發人員認爲，下面描述的各種RDBMS操作類（StoredProcedure類除外）通常可以用直接的JdbcTemplate調用代替。通常，編寫直接在JdbcTemplate上調用方法的DAO方法（與將查詢封裝爲完整的類相對）更簡單。但是，如果通過使用RDBMS操作類獲得可測量的價值，則應繼續使用這些類。"}]}]},{"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、線程安全的類，它封裝了SQL查詢。子類必須實現newRowMapper(..)方法以提供RowMapper實例，該實例可以爲遍歷查詢執行期間創建的ResultSet所獲得的每一行創建一個對象。很少直接使用SqlQuery類，因爲MappingSqlQuery子類爲將行映射到Java類提供了更爲方便的實現。擴展SqlQuery的其他實現是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是可重用的查詢，其中具體的子類必須實現抽象的mapRow(..)方法，以將提供的ResultSet的每一行轉換爲指定類型的對象。以下示例顯示了一個自定義查詢，該查詢將t_actor關係中的數據映射到Actor類的實例："}]},{"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":"該類擴展了使用Actor類型參數化的MappingSqlQuery。此自定義查詢的構造函數將DataSource作爲唯一參數。在此構造函數中，可以使用DataSource和運行的SQL調用超類上的構造函數，以檢索該查詢的行。該SQL用於創建PreparedStatement，因此它可以包含在執行期間要傳遞的任何參數的佔位符。你必須使用傳入SqlParameter的declareParameter方法聲明每個參數。SqlParameter具有名稱，並且具有java.sql.Types中定義的JDBC類型。定義所有參數之後，可以調用compile()方法，以便可以準備並稍後執行。此類在編譯後是線程安全的，因此，只要在初始化DAO時創建這些實例，就可以將它們保留爲實例變量並可以重用。下面的示例演示如何定義此類："}]},{"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":"前面示例中的方法檢索具有作爲唯一參數傳入的id的customer。由於只希望返回一個對象，因此我們以id爲參數調用findObject便捷方法。相反，如果有一個查詢返回一個對象列表並採用其他參數，則將使用其中一種執行方法，該方法採用以可以變參數形式傳入的參數值數組。"}]},{"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類封裝了SQL更新。與查詢一樣，更新對象是可重用的，並且與所有RdbmsOperation類一樣，更新可以具有參數並在SQL中定義。此類提供了許多類似於查詢對象的execute(..)方法的update(..)方法。SQLUpdate類是具體的。可以將其子類化-例如，添加自定義更新方法。但是，你不必子類化SqlUpdate類，因爲可以通過設置SQL和聲明參數來輕鬆地對其進行參數化。以下示例創建一個名爲execute的自定義更新方法："}]},{"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類是RDBMS存儲過程的對象抽象的超類。此類是抽象的，並且其各種execute(..)方法均具有受保護的訪問權限，除了通過提供更嚴格類型的子類之外，還可以防止使用。"}]},{"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":"繼承的sql屬性是RDBMS中存儲過程的名稱。"}]},{"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":"要爲StoredProcedure類定義參數，可以使用SqlParameter或其子類之一。你必須在構造函數中指定參數名稱和SQL類型，如以下代碼片段所示："}]},{"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類型是使用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（帶有SqlParameter）聲明一個IN參數。您可以將IN參數用於存儲過程調用以及使用SqlQuery及其子類（"},{"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":"瞭解SqlQuery"}]},{"type":"text","text":"中介紹）的查詢。"}]},{"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（帶有SqlOutParameter）聲明將在存儲過程調用中使用的out參數。還有一個用於InOut參數的SqlInOutParameter（爲過程提供in值並返回值的參數）。"}]},{"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":"對於in參數，除了名稱和SQL類型外，還可以爲數字數據指定精度，或者爲自定義數據庫類型指定類型名稱。對於out參數，可以提供RowMapper來處理從REF遊標返回的行的映射。另一個選擇是指定一個SqlReturnType，它允許你定義返回值的自定義處理。"}]},{"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":"下一個簡單DAO示例使用StoredProcedure調用任何Oracle數據庫附帶的函數(sysdate())。要使用存儲過程功能，你必須創建一個擴展StoredProcedure的類。在此示例中，StoredProcedure類是一個內部類。但是，如果需要重用StoredProcedure，則可以將其聲明爲頂級類。此示例沒有輸入參數，但是使用SqlOutParameter類將輸出參數聲明爲日期類型。execute()方法將運行該過程，並從結果Map中提取返回的日期。通過使用參數名稱作爲鍵，結果Map爲每個聲明的輸出參數（在這種情況下只有一個）都有一個條目。以下清單顯示了我們的自定義StoredProcedure類："}]},{"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示例包含兩個輸出參數（在本例中爲Oracle REF遊標）："}]},{"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":"請注意如何在TitlesAndGenresStoredProcedure構造函數中使用的clarifyParameter(..)方法的重載變體傳遞給RowMapper實現實例。這是重用現有功能的非常方便且強大的方法。接下來的兩個示例提供了兩個RowMapper實現的代碼。"}]},{"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類將提供的ResultSet中每一行的ResultSet映射到Title域對象，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