clsdatabase.java

java 简单模拟DBMS功能

import java.io.File;
import java.io.FileWriter;

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.Attributes;
import org.xml.sax.helpers.DefaultHandler;

class clsDatabase {
  private String name;

  private String errorMessage;

  LinkedList table;

  public clsDatabase() {
    this.name = new String();
    this.errorMessage = new String();
    table = new LinkedList();
  }

  public String getName() {
    return name;
  }

  public void setName(String newDBName) {
    name = newDBName;
  }

  public int getTableCount() {
    return table.size();
  }

  public int getFieldCount(String tblname) {
    clsTable temp = null;
    int ret = 0;
    try {
      if (existsTable(tblname) == false) {
        errorMessage = "(getFieldCount)Can't find this table!";
      }
      else {
        temp = retTableRef(tblname);
        ret = temp.field.size();
      }
    }
    catch (Exception e) {
      errorMessage = "GetFieldCount Error!\nMessage:" + e;
    }
    finally {

    }
    return ret;
  }

  public void add_table(String tblname) {
    try {
      if (existsTable(tblname) == true || tblname.equals("")) {
        errorMessage = "Table Name Error!!!";
      }
      else {
        table.add(new clsTable(tblname));
      }
    }
    catch (Exception e) {
      errorMessage = "AddTable Error!\nMessage:" + e;
    }
    finally {

    }
  }

  public void del_table(String tblname) {
    try {
      clsTable temp;
      if (existsTable(tblname)) {
        for (int i = 0; i < table.size(); i++) {
          temp = (clsTable) table.get(i);
          if (temp.getName().equals(tblname)) {
            table.remove(i);
            break;
          }
        }
      }
      else {
        errorMessage = "(del_table)Can't find this table!";
      }
    }
    catch (Exception e) {
      errorMessage = "DelTable Error!\nMessage:" + e;
    }
    finally {

    }
  }

  public void add_field(String tblname, String fldname) {
    clsTable temp = null;
    try {
      if (existsTable(tblname) == true && !tblname.equals("")) {
        for (int i = 0; i < table.size(); i++) {
          temp = (clsTable) table.get(i);
          if (existsField(tblname, fldname) == true
              && !fldname.equals("")) {
            errorMessage = "Error Field Name!!!";
          }
          else {
            if (!RowCountLargeThanOne(tblname)) {
              if (temp.getName().equals(tblname)) {
                temp.field.add(new clsField(fldname));
                table.set(i, temp);
                break;
              }
            }
            else {
              errorMessage =
                  "(AddField)About a has row table,you can not add a new field!";
            }
          }
        }
      }
      else {
        errorMessage = "(add_field)Can't find this table!";
      }
    }
    catch (Exception e) {
      errorMessage = "AddField Error!\nMessage:" + e;
    }
    finally {

    }
  }

  public void del_field(String tblname, String fldname) {
    try {
      clsTable temptbl;
      clsField tempfld;
      if (existsTable(tblname) && existsField(tblname, fldname)) {
        for (int k = 0; k < table.size(); k++) {
          temptbl = (clsTable) table.get(k);
          if (temptbl.getName().equals(tblname)) {
            for (int i = 0; i < temptbl.field.size(); i++) {
              tempfld = (clsField) temptbl.field.get(i);
              if (tempfld.getName().equals(fldname)) {
                tempfld.value.clear();
                temptbl.field.set(i, tempfld);
                temptbl.field.remove(i);
                table.set(k, temptbl);
                break;
              }
            }
          }
        }
      }
      else {
        errorMessage = "(del_field)Can't find this table or field!";
      }
    }
    catch (Exception e) {
      errorMessage = "DelField Error!\nMessage:" + e;
    }
    finally {

    }
  }

  public void add_row(String tblname, String value[]) {
    clsField tempfld;
    clsTable temptbl;
    try {
      for (int k = 0; k < table.size(); k++) {
        temptbl = (clsTable) table.get(k);
        if (temptbl.getName().equals(tblname)) {
          if (value.length == temptbl.field.size()) {
            for (int i = 0; i < temptbl.field.size(); i++) {
              tempfld = (clsField) temptbl.field.get(i);
              tempfld.value.add(value[i]);
              temptbl.field.set(i, tempfld);
            }
          }
          table.set(k, temptbl);
          break;
        }
      }
    }
    catch (Exception e) {
      errorMessage = "AddRow Error!\nMessage:" + e.getMessage();
    }
  }

  public void del_row(String tblname, String whereField, String whereValue) {
    clsField tempfld;
    clsTable temptbl;
    String out = new String();
    try {
      if (existsTable(tblname) == true
          && existsField(tblname, whereField) == true) {
        int tempRowIndex;
        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(whereField)) {
                for (int m = 0; m < tempfld.value.size(); m++) {
                  String tempFieldValue = new String();
                  tempFieldValue = (String) tempfld.value
                      .get(m);
                  if (tempFieldValue.equals(whereValue)) {
                    tempRowIndex = m;
                    for (int k = 0; k < temptbl.field
                         .size(); k++) {
                      clsField tempdelrowfld;
                      tempdelrowfld = (clsField) temptbl.field
                          .get(k);
                      tempdelrowfld.value
                          .remove(tempRowIndex);
                      temptbl.field.set(k, tempdelrowfld);
                    }
                    table.set(i, temptbl);
                    break;
                  }
                }
              }
            }
          }
        }
      }
      else {
        errorMessage = "(del_row)Can't find this table or field!";
      }
    }
    catch (Exception e) {
      errorMessage = "DelRow Error!\nMessage:" + e;
    }
    finally {

    }
  }

  public String return_all() {
    String out = new String();
    try {
      out = out + "\n    Database:" + name + "    ";
      out = out + "\n==========START==========";
      for (int i = 0; i < table.size(); i++) {
        clsTable temp = (clsTable) table.get(i);
        clsField tempfld;
        out = out + "\n  Table:" + temp.getName();
        if (temp.field.size() != 0) {
          clsField tempfield = (clsField) temp.field.get(0);
          for (int m = 0; m < tempfield.value.size(); m++) {
            for (int j = 0; j < temp.field.size(); j++) {
              tempfld = (clsField) temp.field.get(j);
              out = out + "\n    " + tempfld.getName() + ":";
              out = out + (String) tempfld.value.get(m);
            }
            out = out + "\n------------------------------";
          }
        }
      }
      out = out + "\n===========END===========\n";
    }
    catch (Exception e) {

    }
    return out;
  }

  public void openDB(String filename) {
    try {
      table.clear();
      setName("");
      if (!filename.equals("") || !new File(filename).exists() == false) {
        File f = new File(filename);
        System.out.println("Loading Database.....");
        SAXParserFactory saxpf = SAXParserFactory.newInstance();
        SAXParser saxparser = saxpf.newSAXParser();
        SaxParser parser1 = new SaxParser(false);
        saxparser.parse(f, parser1);
        SaxParser parser2 = new SaxParser(true);
        saxparser.parse(f, parser2);
        System.out.println("Finish Load Database!");
      }
      else {
        errorMessage = "(OpenDB)File Name Error!";
      }
    }
    catch (Exception e) {
      errorMessage = "OpenDB Error!\nMessage:" + e + "";
    }
    finally {

    }
  }

  public void saveDB(String filename) {
    String headerString = "<?xml version=\"1.0\" encoding=\"gb2312\"?>\n";
    String root = "<Database dbname=\"" + getName() + "\">\n";
    String rootEnd = "</Database>\n";
    String element;
    String elementEnd;
    try {
      File file = new File(filename);
      if (file.exists() == false) {
        file.createNewFile();
      }
        FileWriter fwriter = new FileWriter(file);
        fwriter.write(headerString);
        fwriter.write(root);
        clsTable temptbl;
        clsField tempfld;
        for (int i = 0; i < table.size(); i++) {
          temptbl = retTableRef(i);
          fwriter.write("  <Table tblname=\"" + temptbl.getName()
                        + "\">\n");
          if (temptbl.field.size() > 0
              && ( (clsField) temptbl.field.get(0)).value.size() > 0) {
            for (int j = 0; j < temptbl.field.size(); j++) {
              tempfld = retFieldRef(i, j);
              fwriter.write("    <Field fldname=\"" + tempfld.getName()
                            + "\">\n");
              for (int k = 0; k < ( (clsField) temptbl.field.get(0)).value
                   .size(); k++) {
                fwriter.write("      <Value " + "val=\"" +
                              (tempfld.value.get(k)).toString() + "\" />\n");
              }
              fwriter.write("    </Field>\n");
            }
          }
          fwriter.write("  </Table>\n");
        }
        fwriter.write(rootEnd);
        fwriter.close();
      }
    catch (Exception e) {
      System.out.println("SaveDB Error!!!\nMessage:" + e);
    }
    finally {

    }
  }

  public void setTableName(String oldtblname, String newtblname) {
    try {
      clsTable temptbl;
      if (table.size() > 0 && existsTable(oldtblname)) {
        for (int i = 0; i < table.size(); i++) {
          temptbl = (clsTable) table.get(i);
          if (temptbl.getName() == oldtblname) {
            temptbl.setName(newtblname);
            table.set(i, temptbl);
            break;
          }
        }
      }
      else {
        errorMessage =
            "(setTableName)Can't find this table or haven't any table!";
      }
    }
    catch (Exception e) {
      errorMessage = "SetTableName Error!\nMessage:" + e;
    }
    finally {

    }
  }

  public String getFieldName(String tblname, int fldIndex) {
    String out = new String();
    try {
      clsField tempfld;
      tempfld = retFieldRef(tblname, fldIndex);
      out = tempfld.getName();
    }
    catch (Exception e) {
      errorMessage = "GetFieldName Error!\nMessage:" + e;
    }
    finally {

    }
    return out;
  }

  public boolean RowCountLargeThanOne(String tblname) {
    boolean out = false;
    try {