serialize.java

关系型数据库 Postgresql 6.5.2

package postgresql.util;

import java.io.*;
import java.lang.*;
import java.lang.reflect.*;
import java.net.*;
import java.util.*;
import java.sql.*;

/**
 * This class uses PostgreSQL's object oriented features to store Java Objects.
 *
 * It does this by mapping a Java Class name to a table in the database. Each
 * entry in this new table then represents a Serialized instance of this
 * class. As each entry has an OID (Object IDentifier), this OID can be
 * included in another table.
 *
 * This is too complex to show here, and will be documented in the main
 * documents in more detail.
 *
 */
public class Serialize
{
  // This is the connection that the instance refers to
  protected postgresql.Connection conn;
  
  // This is the table name
  protected String tableName;
  
  // This is the class name
  protected String className;
  
  // This is the Class for this serialzed object
  protected Class ourClass;
  
  /**
   * This creates an instance that can be used to serialize or deserialize
   * a Java object from a PostgreSQL table.
   */
  public Serialize(postgresql.Connection c,String type) throws SQLException
  {
    try {
      conn = c;
      tableName = type.toLowerCase();
      className = toClassName(type);
      ourClass = Class.forName(className);
    } catch(ClassNotFoundException cnfe) {
      throw new PSQLException("postgresql.serial.noclass",type);
    }
    
    // Second check, the type must be a table
    boolean status = false;
    ResultSet rs = conn.ExecSQL("select typname from pg_type,pg_class where typname=relname and typname='"+type+"'");
    if(rs!=null) {
      if(rs.next())
	status=true;
      rs.close();
    }
    // This should never occur, as postgresql has it's own internal checks
    if(!status)
      throw new PSQLException("postgresql.serial.table",type);
    
    // Finally cache the fields within the table
  }
  
  /**
   * This fetches an object from a table, given it's OID
   * @param oid The oid of the object
   * @return Object relating to oid
   * @exception SQLException on error
   */
  public Object fetch(int oid) throws SQLException
  {
    try {
      Object obj = ourClass.newInstance();
      
      // NB: we use java.lang.reflect here to prevent confusion with
      // the postgresql.Field
      java.lang.reflect.Field f[] = ourClass.getDeclaredFields();
      boolean hasOID=false;
      int oidFIELD=-1;
      StringBuffer sb = new StringBuffer("select");
      char sep=' ';
      for(int i=0;i<f.length;i++) {
	String n = f[i].getName();
	if(n.equals("oid")) {
	  hasOID=true;
	  oidFIELD=i;
	}
	sb.append(sep);
	sb.append(n);
	sep=',';
      }
      sb.append(" from ");
      sb.append(tableName);
      sb.append(" where oid=");
      sb.append(oid);
      
      DriverManager.println("store: "+sb.toString());
      ResultSet rs = conn.ExecSQL(sb.toString());
      if(rs!=null) {
	if(rs.next()) {
	  for(int i=0;i<f.length;i++) {
	    f[i].set(obj,rs.getObject(i+1));
	  }
	}
	rs.close();
      } else
       throw new PSQLException("postgresql.unexpected");
      return obj;
    } catch(IllegalAccessException iae) {
      throw new SQLException(iae.toString());
    } catch(InstantiationException ie) {
      throw new SQLException(ie.toString());
    }
  }
  
  /**
   * This stores an object into a table, returning it's OID.<p>
   *
   * If the object has an int called OID, and it is > 0, then
   * that value is used for the OID, and the table will be updated.
   * If the value of OID is 0, then a new row will be created, and the
   * value of OID will be set in the object. This enables an object's
   * value in the database to be updateable.
   *
   * If the object has no int called OID, then the object is stored. However
   * if the object is later retrieved, amended and stored again, it's new
   * state will be appended to the table, and will not overwrite the old
   * entries.
   *
   * @param o Object to store (must implement Serializable)
   * @return oid of stored object
   * @exception SQLException on error
   */
  public int store(Object o) throws SQLException
  {
    try {
      // NB: we use java.lang.reflect here to prevent confusion with
      // the postgresql.Field
      java.lang.reflect.Field f[] = ourClass.getDeclaredFields();
      boolean hasOID=false;
      int oidFIELD=-1;
      boolean update=false;
      
      // Find out if we have an oid value
      for(int i=0;i<f.length;i++) {
	String n = f[i].getName();
	if(n.equals("oid")) {
	  hasOID=true;
	  oidFIELD=i;
	  
	  // We are an update if oid != 0
	  update = f[i].getInt(o)>0;
	}
      }
      
      StringBuffer sb = new StringBuffer(update?"update "+tableName+" set":"insert into "+tableName+" values ");
      char sep=update?' ':'(';
      for(int i=0;i<f.length;i++) {
	String n = f[i].getName();
	sb.append(sep);
	sb.append(n);
	sep=',';
	if(update) {
	  sb.append('=');
	  if(f[i].getType().getName().equals("java.lang.String")) {
	    sb.append('\'');
	    sb.append(f[i].get(o).toString());
	    sb.append('\'');
	  } else
	    sb.append(f[i].get(o).toString());
	}
      }
      
      if(!update) {
	sb.append(") values ");
	sep='(';
	for(int i=0;i<f.length;i++) {
	  String n = f[i].getName();
	  if(f[i].getType().getName().equals("java.lang.String")) {
	    sb.append('\'');
	    sb.append(f[i].get(o).toString());
	    sb.append('\'');
	  } else
	    sb.append(f[i].get(o).toString());
	}
	sb.append(')');
      }
      
      DriverManager.println("store: "+sb.toString());
      ResultSet rs = conn.ExecSQL(sb.toString());
      if(rs!=null) {
	rs.close();
      }
      
      // fetch the OID for returning
      int oid=0;
      if(hasOID) {
	// set the oid in the object
	f[oidFIELD].setInt(o,oid);
      }
      return oid;
      
    } catch(IllegalAccessException iae) {
      throw new SQLException(iae.toString());
    }
  }
  
  /**
   * This method is not used by the driver, but it creates a table, given
   * a Serializable Java Object. It should be used before serializing any
   * objects.
   * @param c Connection to database
   * @param o Object to base table on
   * @exception SQLException on error
   */
  public static void create(postgresql.Connection con,Object o) throws SQLException
  {
    create(con,o.getClass());
  }
  
  /**
   * This method is not used by the driver, but it creates a table, given
   * a Serializable Java Object. It should be used before serializing any
   * objects.
   * @param c Connection to database
   * @param o Class to base table on
   * @exception SQLException on error
   */
  public static void create(postgresql.Connection con,Class c) throws SQLException
  {
    if(c.isInterface())
      throw new PSQLException("postgresql.serial.interface");
    
    // See if the table exists
    String tableName = toPostgreSQL(c.getName());
    
    ResultSet rs = con.ExecSQL("select relname from pg_class where relname = '"+tableName+"'");
    if(!rs.next()) {
      DriverManager.println("found "+rs.getString(1));
      // No entries returned, so the table doesn't exist
      
      StringBuffer sb = new StringBuffer("create table ");
      sb.append(tableName);
      char sep='(';
      
      java.lang.reflect.Field[] fields = c.getDeclaredFields();
      for(int i=0;i<fields.length;i++) {
	Class type = fields[i].getType();
	
	// oid is a special field
	if(!fields[i].getName().equals("oid")) {
	  sb.append(sep);
	  sb.append(fields[i].getName());
	  sb.append(' ');
	  sep=',';
	  
	  if(type.isArray()) {
	    // array handling
	  } else {
	    // convert the java type to postgresql, recursing if a class
	    // is found
	    String n = fields[i].getType().getName();
	    int j=0;
	    for(;j<tp.length && !tp[j][0].equals(n);j++);
	    if(j<tp.length)
	      sb.append(tp[j][1]);
	    else {
	      create(con,fields[i].getType());
	      sb.append(toPostgreSQL(n));
	    }
	  }
	}
      }
      sb.append(")");
      
      // Now create the table
      DriverManager.println("Serialize.create:"+sb);
      con.ExecSQL(sb.toString());
      rs.close();
    } else {
      DriverManager.println("Serialize.create: table "+tableName+" exists, skipping");
    }
  }
  
  // This is used to translate between Java primitives and PostgreSQL types.
  private static final String tp[][] = {
    {"boolean",			"int1"},
    {"double",			"float8"},
    {"float",			"float4"},
    {"int",			"int4"},
    {"long",			"int4"},
    {"short",			"int2"},
    {"java.lang.String",	"text"},
    {"java.lang.Integer",	"int4"},
    {"java.lang.Float",		"float4"},
    {"java.lang.Double",	"float8"},
    {"java.lang.Short",		"int2"}
  };
  
  /**
   * This converts a Java Class name to a postgresql table, by replacing . with
   * _<p>
   *
   * Because of this, a Class name may not have _ in the name.<p>
   * Another limitation, is that the entire class name (including packages)
   * cannot be longer than 32 characters (a limit forced by PostgreSQL).
   *
   * @param name Class name
   * @return PostgreSQL table name
   * @exception SQLException on error
   */
  public static String toPostgreSQL(String name) throws SQLException
  {
    name = name.toLowerCase();
    
    if(name.indexOf("_")>-1)
      throw new PSQLException("postgresql.serial.underscore");
    
    if(name.length()>32)
      throw new PSQLException("postgresql.serial.namelength",name,new Integer(name.length()));
    
    return name.replace('.','_');
  }
  
  
  /**
   * This converts a postgresql table to a Java Class name, by replacing _ with
   * .<p>
   *
   * @param name PostgreSQL table name
   * @return Class name
   * @exception SQLException on error
   */
  public static String toClassName(String name) throws SQLException
  {
    name = name.toLowerCase();
    return name.replace('_','.');
  }
  
}