clsdatabase.java

java 简单模拟DBMS功能

      clsTable temptbl;
      clsField tempfld;
      if (existsTable(tblname)) {
        for (int i = 0; i < table.size(); i++) {
          temptbl = (clsTable) table.get(i);
          if (temptbl.getName().equals(tblname)
              && temptbl.field.size() > 0) {
            for (int j = 0; j < temptbl.field.size(); j++) {
              tempfld = (clsField) temptbl.field.get(i);
              if (tempfld.value.size() == 0) {
                out = false;
              }
              else {
                out = true;
              }
            }
            break;
          }
          else {
            out = false;
          }
        }
      }
      else {
        errorMessage = "(RowCountLargeThanOne)Can't find this table!";
      }
    }
    catch (Exception e) {
      errorMessage = "RowCount Error!\nMessage:" + e;
    }
    finally {

    }
    return out;
  }

  public boolean TableCountLargeThanOne() {
    return (table.size() > 0);
  }

  public boolean FieldCountLargeThanOne(String tblname) {
    boolean out = false;
    try {
      if (existsTable(tblname) == true) {
        for (int i = 0; i < table.size(); i++) {
          clsTable temptbl = (clsTable) table.get(i);
          if (temptbl.field.size() > 0) {
            out = true;
            break;
          }
        }
      }
      else {
        errorMessage = "(FieldCountLargeThanOne)Can't find this table!";
      }
    }
    catch (Exception e) {
      errorMessage = "FieldCount Error!\nMessage:" + e;
    }
    return out;
  }

  public int retTableIndex(String tblname) {
    clsTable temptbl;
    int out = -1;
    try {
      if (existsTable(tblname)) {
        for (int i = 0; i < table.size(); i++) {
          temptbl = (clsTable) table.get(i);
          if (temptbl.getName().equals(tblname)) {
            out = i;
            break;
          }
        }
      }
      else {
        errorMessage = "(retTableIndex)Can't find this table!";
      }
    }
    catch (Exception e) {
      errorMessage = "getTableIndex Error!\nMessage:" + e;
    }
    return out;
  }

  public int retFieldIndex(String tblname, String fldname) {

    clsTable temptbl;
    int out = -1;
    try {
      temptbl = retTableRef(tblname);
      clsField tempfld;
      if (existsTable(tblname) && existsField(tblname, fldname)) {
        for (int i = 0; i < temptbl.field.size(); i++) {
          tempfld = (clsField) temptbl.field.get(i);
          if (tempfld.getName().equals(fldname)) {
            out = i;
            break;
          }
        }
      }
      else {
        errorMessage = "(getFieldIndex)Can't find this table or field!";
      }
    }
    catch (Exception e) {
      errorMessage = "getFieldIndex Error!\nMessage:" + e;
    }
    return out;
  }

  public String getErrorMessage() {
    return errorMessage;
  }

  public void setErrorMessageEmpty() {
    errorMessage = null;
    errorMessage = new String();
  }

  public boolean existsTable(String tblname) {
    clsTable temptbl = null;
    boolean out = false;
    try {
      for (int i = 0; i < table.size(); i++) {
        temptbl = (clsTable) table.get(i);
        if (temptbl.getName().equals(tblname)) {
          out = true;
          break;
        }
      }
    }
    catch (Exception e) {
      errorMessage = "FindTableExists Error!!!";
    }
    return out;
  }

  public boolean existsField(String tblname, String fldname) {
    clsTable temptbl = null;
    clsField tempfld = null;
    boolean out = false;
    try {
      for (int i = 0; i < table.size(); i++) {
        temptbl = (clsTable) table.get(i);
        if (temptbl.getName().equals(tblname)) {
          for (int j = 0; j < temptbl.field.size(); j++) {
            tempfld = (clsField) temptbl.field.get(j);
            if (tempfld.getName().equals(fldname)) {
              out = true;
              break;
            }
          }
        }
      }
    }
    catch (Exception e) {
      errorMessage = "FindFieldExists Error!!!";
    }
    return out;
  }

  public clsTable retTableRef(int tblIndex) {
    clsTable ret = null;
    try {
      if (tblIndex < table.size()) {
        ret = (clsTable) table.get(tblIndex);
      }
      else {
        errorMessage = "(retTableRef)Error Index!";
      }
    }
    catch (Exception e) {
      errorMessage = "getTableRef Error!!!\nMessage:" + e;
    }
    return ret;
  }

  public clsTable retTableRef(String tblname) {
    clsTable ret = null;
    try {
      if (existsTable(tblname)) {
        for (int i = 0; i < table.size(); i++) {
          ret = (clsTable) table.get(i);
          if (ret.getName().equals(tblname)) {
            break;
          }
        }
      }
      else {
        errorMessage = "(retTableRef)Can't find this table!";
      }
    }
    catch (Exception e) {
      errorMessage = "getTableRef Error!!!\nMessage:" + e;
    }
    return ret;
  }

  public clsField retFieldRef(String tblname, String fldname) {
    clsTable temptbl = null;
    clsField ret = null;
    try {
      if (existsField(tblname, fldname)) {
        temptbl = retTableRef(tblname);
        for (int i = 0; i < temptbl.field.size(); i++) {
          ret = (clsField) temptbl.field.get(i);
          if (ret.getName().equals(fldname)) {
            break;
          }
        }
      }
      else {
        errorMessage = "(retFieldRef)Can't find this field!";
      }
    }
    catch (Exception e) {
      errorMessage = "getFieldRef Error!\nMessage:" + e;
    }
    return ret;
  }

  public clsField retFieldRef(String tblname, int fldIndex) {
    clsTable temptbl = null;
    clsField ret = null;
    try {
      if (existsTable(tblname)) {
        temptbl = retTableRef(tblname);
        if (fldIndex < temptbl.field.size()) {
          ret = (clsField) temptbl.field.get(fldIndex);
        }
        else {
          errorMessage = "(retFieldRef)Error Index!";
        }
      }
      else {
        errorMessage = "(retFieldRef)Can't find this table!";
      }
    }
    catch (Exception e) {
      errorMessage = "getFieldRef Error!\nMessage:" + e;
    }
    return ret;
  }

  public clsField retFieldRef(int tblIndex, int fldIndex) {
    clsTable temptbl = null;
    clsField ret = null;
    try {
      if (tblIndex < table.size()) {
        temptbl = retTableRef(tblIndex);
        if (fldIndex < temptbl.field.size()) {
          ret = (clsField) temptbl.field.get(fldIndex);
        }
      }
      else {
        errorMessage = "(retFieldRef)Error Index!";
      }
    }
    catch (Exception e) {
      errorMessage = "getFieldRef Error!\nMessage:" + e;
    }
    return ret;
  }

  public Object[] query(String tblname, String fldname, String fldvalue) {
    LinkedList out = new LinkedList();
    clsField tempfld = retFieldRef(tblname, fldname);
    try {
      if (existsTable(tblname) == true
          && existsField(tblname, fldname) == true) {
        for (int i = 0; i < tempfld.value.size(); i++) {
          if ( ( (String) tempfld.value.get(i)).equals(fldvalue)) {
            out.add( (String) tempfld.value.get(i));
          }
        }
      }
      else {
        errorMessage = "(query)Can't find this table or field!";
      }
    }
    catch (Exception e) {
      errorMessage = "Query Error!\nMessage:" + e;
    }
    return out.toArray();
  }

  public class SaxParser
      extends DefaultHandler {
    private boolean fldstart = false;
    private boolean dbstart = false;
    private boolean tblstart = false;
    private String temptblname = new String();
    private LinkedList fldval = new LinkedList();
    private String tempfldname = new String();
    private boolean ParseValue = false;
    public SaxParser(boolean isParseValue) {
      ParseValue = isParseValue;
    }

    public void startElement(String nsuri, String localName, String qName,
                             Attributes attributes) {
      if (ParseValue == false) {
        if (qName.equals("Database")) {
          dbstart = true;
          setName(attributes.getValue(0));
          System.out.println("Find a Database."
                             + attributes.getValue(0));
        }
        else if (qName.equals("Table")) {
          tblstart = true;
          temptblname = attributes.getValue(0);
          add_table(attributes.getValue(0));
          System.out.println("Find a Table."
                             + attributes.getValue(0));
        }
        else if (qName.equals("Field")) {
          fldstart = true;
          add_field(temptblname, attributes.getValue(0));
          tempfldname = attributes.getValue(0);
          System.out.println("Find a Field."
                             + attributes.getValue(0));
        }
      }
      else {
        if (qName.equals("Table")) {
          tblstart = true;
          temptblname = attributes.getValue(0);
          System.out.println("Find a Table."
                             + attributes.getValue(0));
        }
        else if (qName.equals("Field")) {
          fldstart = true;
          tempfldname = attributes.getValue(0);
          System.out.println("Find a Field."
                             + attributes.getValue(0));
        }
        else if (qName.equals("Value")) {
          if (tblstart == true && fldstart == true) {
            clsTable temptbl = null;
            clsField tempfld = null;
            for (int i = 0; i < table.size(); i++) {
              temptbl = (clsTable) table.get(i);
              if (temptbl.getName().equals(temptblname)) {
                for (int j = 0; j < temptbl.field.size(); j++) {
                  tempfld = (clsField) temptbl.field.get(j);
                  if (tempfld.getName().equals(tempfldname)) {
                    tempfld.value.add(attributes.getValue(0));
                    table.set(i, temptbl);
                    break;
                  }
                }
                break;
              }
            }
            System.out.println("Find a Field Value.");
          }
        }
      }
    }

    public void characters(char[] cha, int start, int length) {

    }

    public void endElement(String nsuri, String localName, String qName) {
      if (qName.equals("Table")) {
        tblstart = false;
        temptblname = "";
        tempfldname = "";
      }
      if (qName.equals("Field")) {
        fldstart = false;
        tempfldname = "";
      }
    }
  }

  public void finalize() {
    name = null;
    table.clear();
    table = null;
    errorMessage = null;
    System.gc();
    Runtime.getRuntime().gc();
  }
}