java.sql.Connection类中有个方法

0 0

java.sql.Connection类中有个方法 10

java.sql.Connection类中有个方法

PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException

这个方法中参数的第二个作用是什么，代表什么意思？

下面是org.springframework.jdbc.core.PreparedStatementCreatorFactory中的一段代码
[code=java]

public PreparedStatement createPreparedStatement(Connection con) throws SQLException {
        PreparedStatement ps = null;
        if (generatedKeysColumnNames != null || returnGeneratedKeys) {
                try {
                        if (generatedKeysColumnNames != null) {
                                ps = con.prepareStatement(this.actualSql, generatedKeysColumnNames);   // TODO
                        }else {
                                ps = con.prepareStatement(this.actualSql, PreparedStatement.RETURN_GENERATED_KEYS);
                        }
                }catch (AbstractMethodError ex) {
                        throw new InvalidDataAccessResourceUsageException(
                                        "The JDBC driver is not compliant to JDBC 3.0 and thus " +
                                        "does not support retrieval of auto-generated keys", ex);
            }
        }
        else if (resultSetType == ResultSet.TYPE_FORWARD_ONLY && !updatableResults) {
                ps = con.prepareStatement(this.actualSql);
        }
        else {
                ps = con.prepareStatement(this.actualSql, resultSetType,
                                updatableResults ? ResultSet.CONCUR_UPDATABLE : ResultSet.CONCUR_READ_ONLY);
        }
        setValues(ps);
        return ps;
}

呵呵，这个问题困惑我许久了！
问题补充

kimmking 写道

finallygo 写道

ms在联合主键的时候用

jdbc规范里，insert时，获取自动添加的keys用的。
但是翻了下mysql 5.1.13 驱动的实现
第二个参数传什么都可以，只要length > 0就可以。

/**
* @see Connection#prepareStatement(String, String[])
*/
public java.sql.PreparedStatement prepareStatement(String sql,
String[] autoGenKeyColNames) throws SQLException {
java.sql.PreparedStatement pStmt = prepareStatement(sql);

((com.mysql.jdbc.PreparedStatement) pStmt)
.setRetrieveGeneratedKeys((autoGenKeyColNames != null)
&& (autoGenKeyColNames.length > 0));

return pStmt;
}

我说为啥，传什么都可以运行的通，呵呵，API说的不是很明白！

Java综合

2011年3月30日 18:25

Technoboy
35
0 0 0

3个答案按时间排序按投票排序

0 0

采纳的答案

finallygo 写道

ms在联合主键的时候用

2011年3月30日 18:25

kimmking
783
0 0 1

添加评论

0 0

ms在联合主键的时候用

2011年3月30日 18:25

finallygo
359
0 0 8

添加评论

0 0

/**
 * Creates a default <code>PreparedStatement</code> object capable
 * of returning the auto-generated keys designated by the given array.
 * This array contains the names of the columns in the target
 * table that contain the auto-generated keys that should be returned.
 * This array is ignored if the SQL
 * statement is not an <code>INSERT</code> statement.
 * 
 * An SQL statement with or without IN parameters can be
 * pre-compiled and stored in a <code>PreparedStatement</code> object. This
 * object can then be used to efficiently execute this statement
 * multiple times.
 * 
 * Note: This method is optimized for handling
 * parametric SQL statements that benefit from precompilation. If
 * the driver supports precompilation,
 * the method <code>prepareStatement</code> will send
 * the statement to the database for precompilation. Some drivers
 * may not support precompilation. In this case, the statement may
 * not be sent to the database until the <code>PreparedStatement</code>
 * object is executed. This has no direct effect on users; however, it does
 * affect which methods throw certain SQLExceptions.
 * 
 * Result sets created using the returned <code>PreparedStatement</code>
 * object will by default be type <code>TYPE_FORWARD_ONLY</code>
 * and have a concurrency level of <code>CONCUR_READ_ONLY</code>.
 *
 * @param sql an SQL statement that may contain one or more '?' IN
 * parameter placeholders
 * @param columnNames an array of column names indicating the columns
 * that should be returned from the inserted row or rows
 * @return a new <code>PreparedStatement</code> object, containing the
 * pre-compiled statement, that is capable of returning the
 * auto-generated keys designated by the given array of column
 * names
 * @exception SQLException if a database access error occurs
 *
 * @since 1.4
 */
 PreparedStatement prepareStatement(String sql, String columnNames[])
throws SQLException;