source: sample/hadoop-0.16/tw/org/nchc/tuple/Schema.java

/*
 * Cloud9: A MapReduce Library for Hadoop
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you
 * may not use this file except in compliance with the License. You may
 * obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0 
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package tw.org.nchc.tuple;

import java.util.HashMap;
import java.util.Map;

import org.apache.hadoop.io.Writable;

/**
 * <p>
 * Description of a Tuple's structure. The Schema class keeps track of column
 * names, data types, and default values. The following code fragment
 * illustrates the use of this class:
 * </p>
 * 
 * <pre>
 * public static final Schema MYSCHEMA = new Schema();
 * static {
 *  MYSCHEMA.addField(&quot;token&quot;, String.class, &quot;&quot;);
 *  MYSCHEMA.addField(&quot;int&quot;, Integer.class, new Integer(1));
 * }
 * </pre>
 * 
 * <p>
 * The following field types are allowed:
 * </p>
 * 
 * <ul>
 * <li>Basic Java primitives: Boolean, Integer, Long, Float, Double, String</li>
 * <li>Classes that implement Writable</li>
 * </ul>
 * 
 * <p>
 * Schema instances can be locked to prevent further changes. Any attempt to
 * alter a locked Schema will result in a runtime exception being thrown. If a
 * Schema is not locked, callers are free to add new fields and edit default
 * values.
 * </p>
 * 
 * <p>
 * New Tuple instances can be created directly from Schema objects through the
 * use of the {@link #instantiate()} method. A call to that method implicitly
 * locks the Schema.
 * </p>
 * 
 * <p>
 * <b>Acknowledgments:</b> much of this code was adapted from the <a
 * href="http://prefuse.org/">Prefuse Visualization Toolkit</a>.
 * </p>
 * 
 */
public class Schema implements Cloneable {

  private String[] mFieldNames;
  private Class<?>[] mFieldTypes;
  private Object[] mDefaultValues;
  private Map<String, Integer> mFieldLookup;
  private int mFieldCount;
  private boolean mLocked;

  // ------------------------------------------------------------------------
  // Constructors

  /**
   * Creates a new empty Schema.
   */
  public Schema() {
    this(10);
  }

  /**
   * Creates a new empty Schema with a starting capacity for a given number of
   * fields.
   * 
   * @param n
   *            the number of columns in this schema
   */
  public Schema(int n) {
    mFieldNames = new String[n];
    mFieldTypes = new Class<?>[n];
    mDefaultValues = new Object[n];
    mFieldCount = 0;
    mLocked = false;
  }

  /**
   * Create a new Schema consisting of the given field names and types.
   * 
   * @param names
   *            the field names
   * @param types
   *            the field types (as Class instances)
   */
  public Schema(String[] names, Class<?>[] types) {
    this(names.length);

    // check the schema validity
    if (names.length != types.length) {
      throw new IllegalArgumentException(
          "Input arrays should be the same length");
    }
    for (int i = 0; i < names.length; ++i) {
      addField(names[i], types[i], null);
    }
  }

  /**
   * Create a new Schema consisting of the given field names, types, and
   * default field values.
   * 
   * @param names
   *            the field names
   * @param types
   *            the field types (as Class instances)
   * @param defaults
   *            the default values for each field
   */
  public Schema(String[] names, Class<?>[] types, Object[] defaults) {
    this(names.length);

    // check the schema validity
    if (names.length != types.length || types.length != defaults.length) {
      throw new IllegalArgumentException(
          "Input arrays should be the same length");
    }
    for (int i = 0; i < names.length; ++i) {
      addField(names[i], types[i], defaults[i]);
    }
  }

  /**
   * Creates a copy of this Schema. Cloned copies of a locked Schema will not
   * inherit the locked status.
   * 
   * @see java.lang.Object#clone()
   */
  public Object clone() {
    Schema s = new Schema(mFieldCount);
    for (int i = 0; i < mFieldCount; ++i) {
      s.addField(mFieldNames[i], mFieldTypes[i], mDefaultValues[i]);
    }
    return s;
  }

  /**
   * Lazily construct the lookup table for this schema. Used to accelerate
   * name-based lookups of schema information.
   */
  protected void initLookup() {
    mFieldLookup = new HashMap<String, Integer>();
    for (int i = 0; i < mFieldNames.length; ++i) {
      mFieldLookup.put(mFieldNames[i], new Integer(i));
    }
  }

  // ------------------------------------------------------------------------
  // Accessors / Mutators

  /**
   * Locks the Schema, preventing any additional changes. Locked Schemas
   * cannot be unlocked! Cloned copies of a locked schema will not inherit
   * this locked status.
   * 
   * @return a reference to this schema
   */
  public Schema lockSchema() {
    mLocked = true;
    return this;
  }

  /**
   * Checks if this schema is locked. Locked Schemas can not be edited.
   * 
   * @return true if this Schema is locked, false otherwise
   */
  public boolean isLocked() {
    return mLocked;
  }

  /**
   * Adds a field to this Schema.
   * 
   * @param name
   *            the field name
   * @param type
   *            the field type (as a Class instance)
   * @throws IllegalArgumentException
   *             if either name or type are null or the name already exists in
   *             this schema.
   */
  public void addField(String name, Class<?> type) {
    addField(name, type, null);
  }

  /**
   * Adds a field to this schema.
   * 
   * @param name
   *            the field name
   * @param type
   *            the field type (as a Class instance)
   * @throws IllegalArgumentException
   *             if either name or type are null or the name already exists in
   *             this schema.
   */
  public void addField(String name, Class<?> type, Object defaultValue) {
    if (!(type == Integer.class || type == Boolean.class
        || type == Long.class || type == Float.class
        || type == Double.class || type == String.class || (!type
        .isInterface() && Writable.class.isAssignableFrom(type)))) {
      throw new SchemaException("Illegal field type: "
          + type.getCanonicalName());
    }

    // check lock status
    if (mLocked) {
      throw new IllegalStateException(
          "Can not add column to a locked Schema.");
    }
    // check for validity
    if (name == null) {
      throw new IllegalArgumentException(
          "Null column names are not allowed.");
    }
    if (type == null) {
      throw new IllegalArgumentException(
          "Null column types are not allowed.");
    }
    for (int i = 0; i < mFieldCount; ++i) {
      if (mFieldNames[i].equals(name)) {
        throw new IllegalArgumentException(
            "Duplicate column names are not allowed: "
                + mFieldNames[i]);
      }
    }

    // resize if necessary
    if (mFieldNames.length == mFieldCount) {
      int capacity = (3 * mFieldNames.length) / 2 + 1;
      String[] names = new String[capacity];
      Class<?>[] types = new Class[capacity];
      Object[] dflts = new Object[capacity];
      System.arraycopy(mFieldNames, 0, names, 0, mFieldCount);
      System.arraycopy(mFieldTypes, 0, types, 0, mFieldCount);
      System.arraycopy(mDefaultValues, 0, dflts, 0, mFieldCount);
      mFieldNames = names;
      mFieldTypes = types;
      mDefaultValues = dflts;
    }

    mFieldNames[mFieldCount] = name;
    mFieldTypes[mFieldCount] = type;
    mDefaultValues[mFieldCount] = defaultValue;

    if (mFieldLookup != null)
      mFieldLookup.put(name, new Integer(mFieldCount));

    mFieldCount++;
  }

  /**
   * Returns the number of fields in this Schema.
   * 
   * @return the number of fields in this Schema
   */
  public int getFieldCount() {
    return mFieldCount;
  }

  /**
   * Returns the name of the field at the given position.
   * 
   * @param index
   *            the field index
   * @return the field name
   */
  public String getFieldName(int index) {
    return mFieldNames[index];
  }

  /**
   * Returns the position of a field given its name.
   * 
   * @param field
   *            the field name
   * @return the field position index
   */
  public int getFieldIndex(String field) {
    if (mFieldLookup == null)
      initLookup();

    Integer idx = (Integer) mFieldLookup.get(field);
    return (idx == null ? -1 : idx.intValue());
  }

  /**
   * Returns the type of the field at the given position.
   * 
   * @param index
   *            the column index
   * @return the column type
   */
  public Class<?> getFieldType(int index) {
    return mFieldTypes[index];
  }

  /**
   * Returns the type of the field given its name.
   * 
   * @param field
   *            the field name
   * @return the field type
   */
  public Class<?> getFieldType(String field) {
    int idx = getFieldIndex(field);
    return (idx < 0 ? null : mFieldTypes[idx]);
  }

  /**
   * Returns the default value of the field at the given position.
   * 
   * @param index
   *            the field index
   * @return the field's default value
   */
  public Object getDefault(int index) {
    return mDefaultValues[index];
  }

  /**
   * Returns the default value of the field with the given name.
   * 
   * @param field
   *            the field name
   * @return the field's default value
   */
  public Object getDefault(String field) {
    int idx = getFieldIndex(field);
    return (idx < 0 ? null : mDefaultValues[idx]);
  }

  /**
   * Sets the default value for the given field.
   * 
   * @param index
   *            the index position of the field to set the default for
   * @param val
   *            the new default value
   */
  public void setDefault(int index, Object val) {
    // check lock status
    if (mLocked) {
      throw new IllegalStateException(
          "Can not update default values of a locked Schema.");
    }
    mDefaultValues[index] = val;
  }

  /**
   * Sets the default value for the given field.
   * 
   * @param field
   *            the name of field to set the default for
   * @param val
   *            the new default value
   */
  public void setDefault(String field, Object val) {
    // check lock status
    if (mLocked) {
      throw new IllegalStateException(
          "Can not update default values of a locked Schema.");
    }
    int idx = getFieldIndex(field);
    mDefaultValues[idx] = val;
  }

  /**
   * Sets the default value for the given field as an <code>int</code>.
   * 
   * @param field
   *            the name of field to set the default for
   * @param val
   *            the new default value
   */
  public void setDefault(String field, int val) {
    setDefault(field, new Integer(val));
  }

  /**
   * Set the default value for the given field as a <code>long</code>.
   * 
   * @param field
   *            the name of field to set the default for
   * @param val
   *            the new default value
   */
  public void setDefault(String field, long val) {
    setDefault(field, new Long(val));
  }

  /**
   * Set the default value for the given field as a <code>float</code>.
   * 
   * @param field
   *            the name of field to set the default for
   * @param val
   *            the new default value
   */
  public void setDefault(String field, float val) {
    setDefault(field, new Float(val));
  }

  /**
   * Set the default value for the given field as a <code>double</code>.
   * 
   * @param field
   *            the name of field to set the default for
   * @param val
   *            the new default value
   */
  public void setDefault(String field, double val) {
    setDefault(field, new Double(val));
  }

  /**
   * Set the default value for the given field as a <code>boolean</code>.
   * 
   * @param field
   *            the name of field to set the default for
   * @param val
   *            the new default value
   */
  public void setDefault(String field, boolean val) {
    setDefault(field, val ? Boolean.TRUE : Boolean.FALSE);
  }

  // ------------------------------------------------------------------------
  // Comparison and Hashing

  /**
   * Compares this Schema with another one for equality.
   */
  public boolean equals(Object o) {
    if (!(o instanceof Schema))
      return false;

    Schema s = (Schema) o;
    if (mFieldCount != s.getFieldCount())
      return false;

    for (int i = 0; i < mFieldCount; ++i) {
      if (!(mFieldNames[i].equals(s.getFieldName(i))
          && mFieldTypes[i].equals(s.getFieldType(i)) && mDefaultValues[i]
          .equals(s.getDefault(i)))) {
        return false;
      }
    }
    return true;
  }

  /**
   * Computes a hashcode for this schema.
   */
  public int hashCode() {
    int hashcode = 0;
    for (int i = 0; i < mFieldCount; ++i) {
      int idx = i + 1;
      int code = idx * mFieldNames[i].hashCode();
      code ^= idx * mFieldTypes[i].hashCode();
      if (mDefaultValues[i] != null)
        code ^= mDefaultValues[i].hashCode();
      hashcode ^= code;
    }
    return hashcode;
  }

  /**
   * Returns a descriptive String for this schema.
   */
  public String toString() {
    StringBuffer sbuf = new StringBuffer();
    sbuf.append("Schema[");
    for (int i = 0; i < mFieldCount; ++i) {
      if (i > 0)
        sbuf.append(' ');
      sbuf.append('(').append(mFieldNames[i]).append(", ");
      sbuf.append(mFieldTypes[i].getName()).append(", ");
      sbuf.append(mDefaultValues[i]).append(')');
    }
    sbuf.append(']');
    return sbuf.toString();
  }

  // ------------------------------------------------------------------------
  // Tuple Operations

  /**
   * Instantiate a new Tuple instance with this Schema. Fields of the newly
   * instantiated Tuple are set to default value.
   * 
   * @return a new Tuple with this Schema
   */
  public Tuple instantiate() {
    lockSchema();

    Object[] objects = new Object[mFieldCount];
    System.arraycopy(mDefaultValues, 0, objects, 0, mFieldCount);

    String[] symbols = new String[mFieldCount];

    String[] fields = new String[mFieldCount];
    System.arraycopy(mFieldNames, 0, fields, 0, mFieldCount);

    Class<?>[] types = new Class<?>[mFieldCount];
    System.arraycopy(mFieldTypes, 0, types, 0, mFieldCount);

    return new Tuple(objects, symbols, fields, types);
  }

  /**
   * Instantiate a new Tuple instance with this Schema.
   * 
   * @param objects
   *            values of each field
   * @return a new Tuple with this Schema
   */
  public Tuple instantiate(Object... objects) {
    lockSchema();

    String[] symbols = new String[mFieldCount];

    String[] fields = new String[mFieldCount];
    System.arraycopy(mFieldNames, 0, fields, 0, mFieldCount);

    Class<?>[] types = new Class[mFieldCount];
    System.arraycopy(mFieldTypes, 0, types, 0, mFieldCount);

    return new Tuple(objects, symbols, fields, types);
  }

} // end of class Schema