Jdbc系列八：批量处理

 当需要成批插入或者更新记录时。可以采用Java的批量更新机制，这一机制允许多条语句一次性提交给数据库批量处理。通常情况下比单独提交处理更有效率。
 JDBC的批量处理语句包括下面两个方法：
  addBatch(String)：添加需要批量处理的SQL语句或是参数；
  executeBatch()：执行批量处理语句；
通常我们会遇到两种批量执行SQL语句的情况：
 多条SQL语句的批量处理；

 一个SQL语句的批量传参；


测试：
 向 Oracle 的 customers 数据表中插入 10 万条记录。测试如何插入, 用时最短。
1、使用 Statement，用时 39567ms

@Test
public void testBatchWithStatement(){
Connection connection = null;
Statement statement = null;
String sql = null;

try {
connection = JDBCTools.getConnection();
JDBCTools.beginTx(connection);

statement = connection.createStatement();

long begin = System.currentTimeMillis();
for(int i = 0; i < 100000; i++){
sql = "INSERT INTO customers VALUES(" + (i + 1)
+ ", 'name_" + i + "', '29-6月 -13')";
statement.addBatch(sql);
}
long end = System.currentTimeMillis();

System.out.println("Time: " + (end - begin)); //39567

JDBCTools.commit(connection);
} catch (Exception e) {
e.printStackTrace();
JDBCTools.rollback(connection);
} finally{
JDBCTools.releaseDB(null, statement, connection);
}
}

2、使用 PreparedStatement。用时 9819ms

@Test
public void testBatchWithPreparedStatement(){
Connection connection = null;
PreparedStatement preparedStatement = null;
String sql = null;

try {
connection = JDBCTools.getConnection();
JDBCTools.beginTx(connection);
sql = "INSERT INTO customers VALUES(?,?,?)";
preparedStatement = connection.prepareStatement(sql);
Date date = new Date(new java.util.Date().getTime());

long begin = System.currentTimeMillis();
for(int i = 0; i < 100000; i++){
preparedStatement.setInt(1, i + 1);
preparedStatement.setString(2, "name_" + i);
preparedStatement.setDate(3, date);

preparedStatement.executeUpdate();
}
long end = System.currentTimeMillis();

System.out.println("Time: " + (end - begin)); //9819

JDBCTools.commit(connection);
} catch (Exception e) {
e.printStackTrace();
JDBCTools.rollback(connection);
} finally{
JDBCTools.releaseDB(null, preparedStatement, connection);
}
}

3、使用Batch批量操作，用时 569ms

@Test
public void testBatch(){
Connection connection = null;
PreparedStatement preparedStatement = null;
String sql = null;

try {
connection = JDBCTools.getConnection();
JDBCTools.beginTx(connection);
sql = "INSERT INTO customers VALUES(?,?,?)";
preparedStatement = connection.prepareStatement(sql);
Date date = new Date(new java.util.Date().getTime());

long begin = System.currentTimeMillis();
for(int i = 0; i < 100000; i++){
preparedStatement.setInt(1, i + 1);
preparedStatement.setString(2, "name_" + i);
preparedStatement.setDate(3, date);

//"积攒" SQL
preparedStatement.addBatch();

//当 "积攒" 到一定程度, 就统一的执行一次. 并且清空先前 "积攒" 的 SQL
if((i + 1) % 300 == 0){
preparedStatement.executeBatch();
preparedStatement.clearBatch();
}
}

//若总条数不是批量数值的整数倍, 则还需要再额外的执行一次.
if(100000 % 300 != 0){
preparedStatement.executeBatch();
preparedStatement.clearBatch();
}

long end = System.currentTimeMillis();

System.out.println("Time: " + (end - begin)); //569

JDBCTools.commit(connection);
} catch (Exception e) {
e.printStackTrace();
JDBCTools.rollback(connection);
} finally{
JDBCTools.releaseDB(null, preparedStatement, connection);
}
}