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| public class Sequence {private final static Log log = LogFactory.getLog(Sequence.class);
private int blockSize = 5;
private long startValue = 0;
private final static String GET_SQL = "select id from sequence_value where name = ?";
private final static String NEW_SQL = "insert into sequence_value (id,name) values (?,?)";
private final static String UPDATE_SQL = "update sequence_value set id = ? where name = ? and id = ?";
private Map<String,Step> stepMap = new HashMap<String, Step>();
private boolean getNextBlock(String sequenceName, Step step) {Long value = getPersistenceValue(sequenceName);
if (value == null) {try {value = newPersistenceValue(sequenceName);
} catch (Exception e) {log.error("newPersistenceValue error!");
value = getPersistenceValue(sequenceName);
}
}
boolean b = saveValue(value,sequenceName) == 1;
if (b) {step.setCurrentValue(value);
step.setEndValue(value+blockSize);
}
return b;
}
public synchronized long get(String sequenceName) {Step step = stepMap.get(sequenceName);
if(step ==null) {step = new Step(startValue,startValue+blockSize);
stepMap.put(sequenceName, step);
} else {if (step.currentValue < step.endValue) {return step.incrementAndGet();
}
}
for (int i = 0; i < blockSize; i++) {if (getNextBlock(sequenceName,step)) {return step.incrementAndGet();
}
}
throw new RuntimeException("No more value.");
}
private int saveValue(long value, String sequenceName) {
Connection connection = null;
PreparedStatement statement = null;
try {connection = dataSource.getConnection();
statement = connection.prepareStatement(UPDATE_SQL);
statement.setLong(1, value + blockSize);
statement.setString(2, sequenceName);
statement.setLong(3, value);
return statement.executeUpdate();} catch (Exception e) {log.error("newPersistenceValue error!", e);
throw new RuntimeException("newPersistenceValue error!", e);
} finally {if (statement != null) {try {statement.close();
} catch (SQLException e) {log.error("close statement error!", e);
}
}
if (connection != null) {try {connection.close();
} catch (SQLException e) {log.error("close connection error!", e);
}
}
}
}
private Long getPersistenceValue(String sequenceName) {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
try {connection = dataSource.getConnection();
statement = connection.prepareStatement(GET_SQL);
statement.setString(1, sequenceName);
resultSet = statement.executeQuery();
if (resultSet.next()) {return resultSet.getLong("id");}
} catch (Exception e) {log.error("getPersistenceValue error!", e);
throw new RuntimeException("getPersistenceValue error!", e);
} finally {if (resultSet != null) {try {resultSet.close();
} catch (SQLException e) {log.error("close resultset error!", e);
}
}
if (statement != null) {try {statement.close();
} catch (SQLException e) {log.error("close statement error!", e);
}
}
if (connection != null) {try {connection.close();
} catch (SQLException e) {log.error("close connection error!", e);
}
}
}
return null;
}
private Long newPersistenceValue(String sequenceName) {
Connection connection = null;
PreparedStatement statement = null;
try {connection = dataSource.getConnection();
statement = connection.prepareStatement(NEW_SQL);
statement.setLong(1, startValue);
statement.setString(2, sequenceName);
statement.executeUpdate();} catch (Exception e) {log.error("newPersistenceValue error!", e);
throw new RuntimeException("newPersistenceValue error!", e);
} finally {if (statement != null) {try {statement.close();
} catch (SQLException e) {log.error("close statement error!", e);
}
}
if (connection != null) {try {connection.close();
} catch (SQLException e) {log.error("close connection error!", e);
}
}
}
return startValue;
}
private DataSource dataSource;
public void setDataSource(DataSource dataSource) {this.dataSource = dataSource;}
public void setBlockSize(int blockSize) {this.blockSize = blockSize;}
public void setStartValue(long startValue) {this.startValue = startValue;}
static class Step {
private long currentValue;
private long endValue;
Step(long currentValue, long endValue) {
this.currentValue = currentValue;
this.endValue = endValue;
}
public void setCurrentValue(long currentValue) {this.currentValue = currentValue;}
public void setEndValue(long endValue) {this.endValue = endValue;}
public long incrementAndGet() {return ++currentValue;}
}
}
|
