Java ，druid 解析sql，并通过 feign接口查询到的表元数据，替换包含left join 的select sql语句中的*，支持mysql、hive、postgresql、oracle、sqlserver等多种数据库。需要写出代码

下面是使用Java和Druid实现解析SQL语句，并通过Feign接口查询表元数据，替换包含left join的select语句中的*的示例代码：

import com.alibaba.druid.sql.SQLUtils;
import com.alibaba.druid.sql.ast.SQLExpr;
import com.alibaba.druid.sql.ast.SQLJoinTableSource;
import com.alibaba.druid.sql.ast.SQLStatement;
import com.alibaba.druid.sql.ast.expr.SQLIdentifierExpr;
import com.alibaba.druid.sql.ast.statement.SQLSelect;
import com.alibaba.druid.sql.ast.statement.SQLSelectItem;
import com.alibaba.druid.sql.ast.statement.SQLSelectQueryBlock;
import com.alibaba.druid.sql.ast.statement.SQLTableSource;
import com.alibaba.druid.sql.dialect.mysql.ast.statement.MySqlSelectQueryBlock;
import com.alibaba.druid.sql.dialect.mysql.visitor.MySqlOutputVisitor;
import com.alibaba.druid.util.JdbcConstants;

import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class SqlParser {
    private static final String DB_TYPE_MYSQL = "mysql";
    private static final String DB_TYPE_ORACLE = "oracle";
    private static final String DB_TYPE_POSTGRESQL = "postgresql";
    private static final String DB_TYPE_SQLSERVER = "sqlserver";
    private static final String DB_TYPE_HIVE = "hive";

    private static final Pattern LEFT_JOIN_PATTERN = Pattern.compile("(?i)\\b(left join)\\b");

    private FeignClient feignClient; // Feign接口

    public void parseAndReplaceSql(String sql, String dbType) {
        // 解析SQL语句
        List<SQLStatement> sqlStatements = SQLUtils.parseStatements(sql, dbType);

        for (SQLStatement statement : sqlStatements) {
            // 只处理SELECT语句
            if (statement instanceof SQLSelect) {
                SQLSelect select = (SQLSelect) statement;
                SQLSelectQueryBlock queryBlock = (SQLSelectQueryBlock) select.getQuery();

                // 获取所有SELECT项
                List<SQLSelectItem> selectItems = queryBlock.getSelectList();

                // 判断是否包含LEFT JOIN
                boolean hasLeftJoin = false;
                SQLTableSource from = queryBlock.getFrom();
                if (from instanceof SQLJoinTableSource) {
                    SQLJoinTableSource join = (SQLJoinTableSource) from;
                    if (join.getJoinType().getName().equalsIgnoreCase("left join")) {
                        hasLeftJoin = true;
                    }
                }

                // 如果包含LEFT JOIN，则替换SELECT项中的*
                if (hasLeftJoin) {
                    for (int i = 0; i < selectItems.size(); i++) {
                        SQLSelectItem item = selectItems.get(i);
                        SQLExpr expr = item.getExpr();
                        if (expr instanceof SQLIdentifierExpr && ((SQLIdentifierExpr) expr).getName().equals("*")) {
                            // 调用Feign接口查询表元数据，替换SELECT项中的*
                            String tableName = ((SQLIdentifierExpr) from).getName(); // 获取表名
                            List<TableColumn> columns = feignClient.getTableColumns(tableName);
                            StringBuilder sb = new StringBuilder();
                            for (TableColumn column : columns) {
                                sb.append(column.getColumnName()).append(",");
                            }
                            sb.deleteCharAt(sb.length() - 1);
                            item.setExpr(SQLUtils.toSQLExpr(sb.toString(), dbType));
                            selectItems.set(i, item);
                        }
                    }
                }
            }
        }

        // 生成替换后的SQL语句
        String resultSql = SQLUtils.toSQLString(sqlStatements, dbType, new MySqlOutputVisitor());
        System.out.println(resultSql);
    }
}

// 表元数据
class TableColumn {
    private String columnName;
    private String columnType;

    // getter/setter
}

// Feign接口
@FeignClient(name = "metadata-service")
public interface FeignClient {
    @GetMapping("/tableColumns")
    List<TableColumn> getTableColumns(@RequestParam("tableName") String tableName);
}

需要注意的是，上述代码中的`FeignClient`是使用Spring Cloud Feign实现的，需要在项目中引入相应的依赖。同时，`getTableColumns`方法需要根据实际情况进行修改，具体实现可以参考Feign的使用文档。