Java tutorial
/* * Copyright 2002-2018 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.jdbc.support.incrementer; import java.sql.Connection; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import javax.sql.DataSource; import org.springframework.dao.DataAccessException; import org.springframework.dao.DataAccessResourceFailureException; import org.springframework.jdbc.datasource.DataSourceUtils; import org.springframework.jdbc.support.JdbcUtils; /** * {@link DataFieldMaxValueIncrementer} that increments the maximum value of a given MySQL table * with the equivalent of an auto-increment column. Note: If you use this class, your MySQL * key column should <i>NOT</i> be auto-increment, as the sequence table does the job. * * <p>The sequence is kept in a table; there should be one sequence table per * table that needs an auto-generated key. The storage engine used by the sequence table * can be MYISAM or INNODB since the sequences are allocated using a separate connection * without being affected by any other transactions that might be in progress. * * <p>Example: * * <pre class="code">create table tab (id int unsigned not null primary key, text varchar(100)); * create table tab_sequence (value int not null); * insert into tab_sequence values(0);</pre> * * If "cacheSize" is set, the intermediate values are served without querying the * database. If the server or your application is stopped or crashes or a transaction * is rolled back, the unused values will never be served. The maximum hole size in * numbering is consequently the value of cacheSize. * * <p>It is possible to avoid acquiring a new connection for the incrementer by setting the * "useNewConnection" property to false. In this case you <i>MUST</i> use a non-transactional * storage engine like MYISAM when defining the incrementer table. * * @author Jean-Pierre Pawlak * @author Thomas Risberg * @author Juergen Hoeller */ public class MySQLMaxValueIncrementer extends AbstractColumnMaxValueIncrementer { /** The SQL string for retrieving the new sequence value. */ private static final String VALUE_SQL = "select last_insert_id()"; /** The next id to serve. */ private long nextId = 0; /** The max id to serve. */ private long maxId = 0; /** Whether or not to use a new connection for the incrementer. */ private boolean useNewConnection = true; /** * Default constructor for bean property style usage. * @see #setDataSource * @see #setIncrementerName * @see #setColumnName */ public MySQLMaxValueIncrementer() { } /** * Convenience constructor. * @param dataSource the DataSource to use * @param incrementerName the name of the sequence table to use * @param columnName the name of the column in the sequence table to use */ public MySQLMaxValueIncrementer(DataSource dataSource, String incrementerName, String columnName) { super(dataSource, incrementerName, columnName); } /** * Set whether to use a new connection for the incrementer. * <p>{@code true} is necessary to support transactional storage engines, * using an isolated separate transaction for the increment operation. * {@code false} is sufficient if the storage engine of the sequence table * is non-transactional (like MYISAM), avoiding the effort of acquiring an * extra {@code Connection} for the increment operation. * <p>Default is {@code true} since Spring Framework 5.0. * @since 4.3.6 * @see DataSource#getConnection() */ public void setUseNewConnection(boolean useNewConnection) { this.useNewConnection = useNewConnection; } @Override protected synchronized long getNextKey() throws DataAccessException { if (this.maxId == this.nextId) { /* * If useNewConnection is true, then we obtain a non-managed connection so our modifications * are handled in a separate transaction. If it is false, then we use the current transaction's * connection relying on the use of a non-transactional storage engine like MYISAM for the * incrementer table. We also use straight JDBC code because we need to make sure that the insert * and select are performed on the same connection (otherwise we can't be sure that last_insert_id() * returned the correct value). */ Connection con = null; Statement stmt = null; boolean mustRestoreAutoCommit = false; try { if (this.useNewConnection) { con = getDataSource().getConnection(); if (con.getAutoCommit()) { mustRestoreAutoCommit = true; con.setAutoCommit(false); } } else { con = DataSourceUtils.getConnection(getDataSource()); } stmt = con.createStatement(); if (!this.useNewConnection) { DataSourceUtils.applyTransactionTimeout(stmt, getDataSource()); } // Increment the sequence column... String columnName = getColumnName(); try { stmt.executeUpdate("update " + getIncrementerName() + " set " + columnName + " = last_insert_id(" + columnName + " + " + getCacheSize() + ")"); } catch (SQLException ex) { throw new DataAccessResourceFailureException("Could not increment " + columnName + " for " + getIncrementerName() + " sequence table", ex); } // Retrieve the new max of the sequence column... ResultSet rs = stmt.executeQuery(VALUE_SQL); try { if (!rs.next()) { throw new DataAccessResourceFailureException( "last_insert_id() failed after executing an update"); } this.maxId = rs.getLong(1); } finally { JdbcUtils.closeResultSet(rs); } this.nextId = this.maxId - getCacheSize() + 1; } catch (SQLException ex) { throw new DataAccessResourceFailureException("Could not obtain last_insert_id()", ex); } finally { JdbcUtils.closeStatement(stmt); if (con != null) { if (this.useNewConnection) { try { con.commit(); if (mustRestoreAutoCommit) { con.setAutoCommit(true); } } catch (SQLException ignore) { throw new DataAccessResourceFailureException( "Unable to commit new sequence value changes for " + getIncrementerName()); } JdbcUtils.closeConnection(con); } else { DataSourceUtils.releaseConnection(con, getDataSource()); } } } } else { this.nextId++; } return this.nextId; } }