Java 通过JDBC查询数据库表结构(字段名称,类型,长度等)

我们如何知道，我们访问的数据库的表，有哪些字段，字段的类型是什么，长度限制是什么？

在实际工作中，我就遇到过，要做动态sql，比如insert，如果是数字就不要加引号，如果是字符就要加引号，还比如做基于数据库表的代码生成器等。我们都可能需要查表的表结构。

下面我就介绍一种通过JAVA最原始的JDBC查表结构的方法。

Java 通过JDBC查询数据库表结构(字段名称,类型,长度等)

在JDBC中，PreparedStatement.executeQuery().getMetaData();后，我们可以通过ResultSetMetaData对象查询返回结果集的源数据信息，也就是表结构信息。

示例代码如下：

 

 

package astar.sutil.db;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

/**  
* @author 鲁炬
*
*/
public class DbMetaDataUtilTest {

  public static void main(String[] args) throws SQLException, ClassNotFoundException {
    String user = "user";
    String password = "pwd";
    String jdbcDriver = "com.ibm.db2.jcc.DB2Driver";
    String jdbcUrl = "jdbc:db2://localhost:50000/DBNAME";
    Connection conn = null;
    Class.forName(jdbcDriver);
    conn = DriverManager.getConnection(jdbcUrl, user, password);

    PreparedStatement pst = null;
    try {
      pst = conn.prepareStatement("select * from t_table where 1=2");
      ResultSetMetaData rsd = pst.executeQuery().getMetaData();
      for(int i = 0; i < rsd.getColumnCount(); i++) {
        System.out.print("java类型："+rsd.getColumnClassName(i + 1));
        System.out.print("  数据库类型:"+rsd.getColumnTypeName(i + 1));
        System.out.print("  字段名称:"+rsd.getColumnName(i + 1));
        System.out.print("  字段长度:"+rsd.getColumnDisplaySize(i + 1));
        System.out.println();
      }
    } catch(SQLException e) {
      throw new RuntimeException(e);
    } finally {
      try {
        pst.close();
        pst = null;
      } catch(SQLException e) {
        throw new RuntimeException(e);
      }
    }

  }

}

 

以上代码运行打印如下：

 

java类型：java.lang.String  数据库类型:VARCHAR  字段名称:CORP_CODE  字段名称:20
java类型：java.lang.String  数据库类型:VARCHAR  字段名称:CORP_NAME  字段名称:100
java类型：java.lang.String  数据库类型:VARCHAR  字段名称:SIMPLY_NAME  字段名称:50
java类型：java.lang.String  数据库类型:CHAR  字段名称:CORP_LEVEL  字段名称:1
java类型：java.lang.String  数据库类型:VARCHAR  字段名称:SUP_CORP_CODE  字段名称:20
java类型：java.lang.String  数据库类型:VARCHAR  字段名称:PROVINCE  字段名称:8
java类型：java.lang.String  数据库类型:VARCHAR  字段名称:STAT_CODE  字段名称:8
java类型：java.lang.String  数据库类型:CHAR  字段名称:CORP_KIND  字段名称:4
java类型：java.lang.String  数据库类型:CHAR  字段名称:IS_LEAF  字段名称:1
java类型：java.lang.String  数据库类型:CHAR  字段名称:IS_USE  字段名称:1
java类型：java.lang.String  数据库类型:CHAR  字段名称:IS_UPDATE  字段名称:1
java类型：java.lang.Integer  数据库类型:SMALLINT  字段名称:ORDER_CODE  字段名称:6
java类型：java.lang.String  数据库类型:VARCHAR  字段名称:MAP_REGIE_CODE  字段名称:20
java类型：java.lang.String  数据库类型:CHAR  字段名称:IS_SUPER  字段名称:1
java类型：java.lang.Integer  数据库类型:SMALLINT  字段名称:DISPLAY_ID  字段名称:6
java类型：java.lang.String  数据库类型:CHAR  字段名称:IS_GIS  字段名称:1

 

更多详细的属性输出可以读一下ResultSetMetaData对象的源码。

 

/*
 * @(#)ResultSetMetaData.java	1.33 05/12/01
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.sql;

/**
 * An object that can be used to get information about the types 
 * and properties of the columns in a ResultSet object.
 * The following code fragment creates the ResultSet object rs,
 * creates the ResultSetMetaData object rsmd, and uses rsmd
 * to find out how many columns rs has and whether the first column in rs
 * can be used in a WHERE clause.
 * 
 *
 *     ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
 *     ResultSetMetaData rsmd = rs.getMetaData();
 *     int numberOfColumns = rsmd.getColumnCount();
 *     boolean b = rsmd.isSearchable(1);
 *
 * 
 */

public interface ResultSetMetaData extends Wrapper {

    /**
     * Returns the number of columns in this ResultSet object.
     *
     * @return the number of columns
     * @exception SQLException if a database access error occurs
     */
    int getColumnCount() throws SQLException;

    /**
     * Indicates whether the designated column is automatically numbered.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return true if so; false otherwise
     * @exception SQLException if a database access error occurs
     */
    boolean isAutoIncrement(int column) throws SQLException;

    /**
     * Indicates whether a column's case matters.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return true if so; false otherwise
     * @exception SQLException if a database access error occurs
     */
    boolean isCaseSensitive(int column) throws SQLException;	

    /**
     * Indicates whether the designated column can be used in a where clause.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return true if so; false otherwise
     * @exception SQLException if a database access error occurs
     */
    boolean isSearchable(int column) throws SQLException;

    /**
     * Indicates whether the designated column is a cash value.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return true if so; false otherwise
     * @exception SQLException if a database access error occurs
     */
    boolean isCurrency(int column) throws SQLException;

    /**
     * Indicates the nullability of values in the designated column.		
     *
     * @param column the first column is 1, the second is 2, ...
     * @return the nullability status of the given column; one of columnNoNulls,
     *          columnNullable or columnNullableUnknown
     * @exception SQLException if a database access error occurs
     */
    int isNullable(int column) throws SQLException;

    /**
     * The constant indicating that a
     * column does not allow NULL values.
     */
    int columnNoNulls = 0;

    /**
     * The constant indicating that a
     * column allows NULL values.
     */
    int columnNullable = 1;

    /**
     * The constant indicating that the
     * nullability of a column's values is unknown.
     */
    int columnNullableUnknown = 2;

    /**
     * Indicates whether values in the designated column are signed numbers.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return true if so; false otherwise
     * @exception SQLException if a database access error occurs
     */
    boolean isSigned(int column) throws SQLException;

    /**
     * Indicates the designated column's normal maximum width in characters.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return the normal maximum number of characters allowed as the width
     *          of the designated column
     * @exception SQLException if a database access error occurs
     */
    int getColumnDisplaySize(int column) throws SQLException;

    /**
     * Gets the designated column's suggested title for use in printouts and
     * displays. The suggested title is usually specified by the SQL AS 
     * clause.  If a SQL AS is not specified, the value returned from 
     * getColumnLabel will be the same as the value returned by the 
     * getColumnName method.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return the suggested column title
     * @exception SQLException if a database access error occurs
     */
    String getColumnLabel(int column) throws SQLException;	

    /**
     * Get the designated column's name.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return column name
     * @exception SQLException if a database access error occurs
     */
    String getColumnName(int column) throws SQLException;

    /**
     * Get the designated column's table's schema.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return schema name or "" if not applicable
     * @exception SQLException if a database access error occurs
     */
    String getSchemaName(int column) throws SQLException;

    /**
     * Get the designated column's specified column size. 
     * For numeric data, this is the maximum precision.  For character data, this is the length in characters. 
     * For datetime datatypes, this is the length in characters of the String representation (assuming the 
     * maximum allowed precision of the fractional seconds component). For binary data, this is the length in bytes.  For the ROWID datatype, 
     * this is the length in bytes. 0 is returned for data types where the
     * column size is not applicable.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return precision
     * @exception SQLException if a database access error occurs
     */
    int getPrecision(int column) throws SQLException;

    /**
     * Gets the designated column's number of digits to right of the decimal point.
     * 0 is returned for data types where the scale is not applicable.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return scale
     * @exception SQLException if a database access error occurs
     */
    int getScale(int column) throws SQLException;	

    /**
     * Gets the designated column's table name. 
     *
     * @param column the first column is 1, the second is 2, ...
     * @return table name or "" if not applicable
     * @exception SQLException if a database access error occurs
     */
    String getTableName(int column) throws SQLException;

    /**
     * Gets the designated column's table's catalog name.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return the name of the catalog for the table in which the given column
     *          appears or "" if not applicable
     * @exception SQLException if a database access error occurs
     */
    String getCatalogName(int column) throws SQLException;

    /**
     * Retrieves the designated column's SQL type.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return SQL type from java.sql.Types
     * @exception SQLException if a database access error occurs
     * @see Types
     */
    int getColumnType(int column) throws SQLException;

    /**
     * Retrieves the designated column's database-specific type name.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return type name used by the database. If the column type is
     * a user-defined type, then a fully-qualified type name is returned.
     * @exception SQLException if a database access error occurs
     */
    String getColumnTypeName(int column) throws SQLException;

    /**
     * Indicates whether the designated column is definitely not writable.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return true if so; false otherwise
     * @exception SQLException if a database access error occurs
     */
    boolean isReadOnly(int column) throws SQLException;

    /**
     * Indicates whether it is possible for a write on the designated column to succeed.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return true if so; false otherwise
     * @exception SQLException if a database access error occurs
     */
    boolean isWritable(int column) throws SQLException;

    /**
     * Indicates whether a write on the designated column will definitely succeed.	
     *
     * @param column the first column is 1, the second is 2, ...
     * @return true if so; false otherwise
     * @exception SQLException if a database access error occurs
     */
    boolean isDefinitelyWritable(int column) throws SQLException;

    //--------------------------JDBC 2.0-----------------------------------

    /**
     * 
Returns the fully-qualified name of the Java class whose instances 
     * are manufactured if the method ResultSet.getObject
     * is called to retrieve a value 
     * from the column.  ResultSet.getObject may return a subclass of the
     * class returned by this method.
     *
     * @param column the first column is 1, the second is 2, ...
     * @return the fully-qualified name of the class in the Java programming
     *         language that would be used by the method 
     * ResultSet.getObject to retrieve the value in the specified
     * column. This is the class name used for custom mapping.
     * @exception SQLException if a database access error occurs
     * @since 1.2
     */
    String getColumnClassName(int column) throws SQLException;
}