sequence.java

办公自动化项目

package hong.javanet.dao.util;

import java.sql.*;
import java.util.*;
import org.hibernate.*;
import hong.javanet.dao.*;

public class Sequence {

    private String name;
    private int currentID;
    static private HashMap sequences = new HashMap();
    public int CACHE = 100;
    public boolean DEBUG = true;

    protected Connection getConnection() {
        try {
          return HibernateUtil.currentSession().connection();
        }
        catch (HibernateException ex) {
          return null;
        }
    }

    private Sequence(String name) {
        if(this.DEBUG) {
            this.CACHE = 1;
        }
        try {
            this.name = name;
            Connection con = this.getConnection();
            PreparedStatement psSelect = con.prepareStatement(
                    "select value from mysequence where name=?");
            psSelect.setString(1, name);
            ResultSet rs = psSelect.executeQuery();
            if (rs.next()) {
                this.currentID = rs.getInt(1);
                psSelect.close();
                rs.close();
            } else {
                PreparedStatement psInsert = con.prepareStatement(
                        "insert into mysequence(name,value) values(?,?)");
                psInsert.setString(1, name);
                psInsert.setInt(2, 0);
                int rowcount = psInsert.executeUpdate();
                psInsert.close();
                if (rowcount == 0) {
                    throw new RuntimeException("创建序列 "+this.name+" 出错！:" + name);
                }
                this.currentID = 0;
            }
        } catch (SQLException ex) {
            throw new RuntimeException("创建序列 "+this.name+" 出错！:" + ex.getMessage(), ex);
        }
    }

    public synchronized int nextVal() {
        try {
            if (this.currentID % this.CACHE == 0) {
                PreparedStatement ps = this.getConnection().prepareStatement(
                        "update mysequence set value=value+? where name=?");
                ps.setInt(1, this.CACHE);
                ps.setString(2, this.name);
                int row = ps.executeUpdate();
                ps.close();
                if (row == 0) {
                    throw new RuntimeException("序列 "+this.name+" 应该存在，但是可能不存在！");
                }

                if(this.DEBUG) {
                    ps = this.getConnection().prepareStatement(
                            "select value from mysequence where name=?");
                    ps.setString(1, this.name);
                    ResultSet rs = ps.executeQuery();
                    if (rs.next()) {
                        this.currentID = rs.getInt(1) - this.CACHE;
                    } else {
                        throw new RuntimeException("序列 " + this.name +
                                " 应该存在，但是可能不存在！");
                    }
                }
            }
            return ++this.currentID;
        } catch (SQLException ex) {
            throw new RuntimeException("取序列 "+this.name+" 值出错！" + ex.getMessage(), ex);
        }
    }


    public static synchronized Sequence getInstance(String name) {
        name = name.toLowerCase();
        Sequence seq = (Sequence) sequences.get(name);
        if (seq == null) {
            seq = new Sequence(name);
            sequences.put(name,seq);
        }
        return seq;
    }
}