【JDBC/Oracle】利用MetaData获得一张表的所有字段

本文例程下载：https://files.cnblogs.com/files/heyang78/ufo_meta_tableColumns_210928.rar

一般来说先有的表后有的Mapper文件，但也有反过来的，今天我就遇到了，在Mapper.xml能找到表名，也有DB可以执行SQL，表字段及说明却无处可寻，只能自己逆向建立起来。

以前曾经做过一个以MetaData取表字段和注释的程序，今天拿它改写一回，便有了下面的程序：

package ufo;

import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Set;
import java.util.TreeSet;

public class TableFieldCounter {
    //-- 以下为连接Oracle数据库的四大参数
    private static final String DRIVER = "oracle.jdbc.driver.OracleDriver";
    private static final String URL = "jdbc:oracle:thin:@127.0.0.1:1521:orclhy78";
    private static final String USER = "luna";
    private static final String PSWD = "1234";
    
    /**
     * 批量打印表和列名
     * @param tableNames
     */
    public void printColumnsIn(String... tableNames) {
        Connection conn = null;
        
        try{
            Class.forName(DRIVER);
            conn = DriverManager.getConnection(URL, USER, PSWD);
            
            for(String tableName:tableNames) {
                if(tableName.trim().length()>0) {
                    Set<String> set=findColumnsIn(tableName,conn);
                    
                    System.out.println("
Table:"+tableName.toUpperCase());
                    for(String col:set) {
                        System.out.println("    "+col);
                    }
                }
            }
            
            
        } catch (Exception e) {
            System.out.print(e.getMessage());
        } finally {
            try {
                conn.close();
            } catch (SQLException e) {
                System.out.print("Can't close stmt/conn because of " + e.getMessage());
            }
        }
    }
    
    /**
     * 得到一张表的字段，按字母序排列
     * @param tableName
     * @param conn
     * @return
     * @throws Exception
     */
    private Set<String> findColumnsIn(String tableName,Connection conn) throws Exception{
        DatabaseMetaData dbmd = conn.getMetaData();
        
        ResultSet rs = dbmd.getColumns(null,"%",tableName.toUpperCase(),"%");// 注意%不该改

        Set<String> set=new TreeSet<String>();
        while(rs.next()) {
            set.add(rs.getString("COLUMN_NAME"));// 注意COLUMN_NAME不该改
        }
        
        return set;
    }
    
    /**
     * 执行点
     * @param args
     */
    public static void main(String[] args) {
        TableFieldCounter tfc=new TableFieldCounter();
        tfc.printColumnsIn("emp","testtb","");
    }
}

执行结果：

Table:EMP
    AGE
    ID
    NAME

Table:TESTTB
    AGE
    COL1
    COL2
    COL3
    ID
    NAME
    SEX

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