java 回调 spring jdbc 查询模板
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2022-07-13 16:01:25
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spring jdbc 查询模板 内部类的使用
感觉这种写法让代码显得很清晰,将固定的操作步骤制定成模板方法,通过使用者,自己来实现继承类来决定操作过程。
org.springframework.jdbc.core.RowMapper
org.springframework.jdbc.core.RowMapperResultSetExtractor
以下是模板类的操作过程:
org.springframework.jdbc.core.JdbcTemplate
感觉这种写法让代码显得很清晰,将固定的操作步骤制定成模板方法,通过使用者,自己来实现继承类来决定操作过程。
org.springframework.jdbc.core.RowMapper
public interface RowMapper<T> { T mapRow(ResultSet rs, int rowNum) throws SQLException; }
org.springframework.jdbc.core.RowMapperResultSetExtractor
public class RowMapperResultSetExtractor<T> implements ResultSetExtractor<List<T>> { public List<T> extractData(ResultSet rs) throws SQLException { List<T> results = (this.rowsExpected > 0 ? new ArrayList<T>(this.rowsExpected) : new ArrayList<T>()); int rowNum = 0; while (rs.next()) { results.add(this.rowMapper.mapRow(rs, rowNum++)); } return results; } }
以下是模板类的操作过程:
org.springframework.jdbc.core.JdbcTemplate
public <T> List<T> query(String sql, RowMapper<T> rowMapper) throws DataAccessException { return query(sql, new RowMapperResultSetExtractor<T>(rowMapper)); } public <T> T query(final String sql, final ResultSetExtractor<T> rse) throws DataAccessException { Assert.notNull(sql, "SQL must not be null"); Assert.notNull(rse, "ResultSetExtractor must not be null"); if (logger.isDebugEnabled()) { logger.debug("Executing SQL query [" + sql + "]"); } class QueryStatementCallback implements StatementCallback<T>, SqlProvider { public T doInStatement(Statement stmt) throws SQLException { ResultSet rs = null; try { rs = stmt.executeQuery(sql); ResultSet rsToUse = rs; if (nativeJdbcExtractor != null) { rsToUse = nativeJdbcExtractor.getNativeResultSet(rs); } return rse.extractData(rsToUse); } finally { JdbcUtils.closeResultSet(rs); } } public String getSql() { return sql; } } return execute(new QueryStatementCallback()); } //模板方法 public <T> T execute(StatementCallback<T> action) throws DataAccessException { Assert.notNull(action, "Callback object must not be null"); Connection con = DataSourceUtils.getConnection(getDataSource()); Statement stmt = null; try { Connection conToUse = con; if (this.nativeJdbcExtractor != null && this.nativeJdbcExtractor.isNativeConnectionNecessaryForNativeStatements()) { conToUse = this.nativeJdbcExtractor.getNativeConnection(con); } stmt = conToUse.createStatement(); applyStatementSettings(stmt); Statement stmtToUse = stmt; if (this.nativeJdbcExtractor != null) { stmtToUse = this.nativeJdbcExtractor.getNativeStatement(stmt); } T result = action.doInStatement(stmtToUse); handleWarnings(stmt); return result; } catch (SQLException ex) { // Release Connection early, to avoid potential connection pool deadlock // in the case when the exception translator hasn't been initialized yet. JdbcUtils.closeStatement(stmt); stmt = null; DataSourceUtils.releaseConnection(con, getDataSource()); con = null; throw getExceptionTranslator().translate("StatementCallback", getSql(action), ex); } finally { JdbcUtils.closeStatement(stmt); DataSourceUtils.releaseConnection(con, getDataSource()); } }