src/java/org/apache/hcatalog/data/schema/HCatSchema.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.hcatalog.data.schema;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.hcatalog.common.HCatException;

/**
 * HCatSchema. This class is NOT thread-safe.
 */

public class HCatSchema implements Serializable {

    private static final long serialVersionUID = 1L;

    private final List<HCatFieldSchema> fieldSchemas;
    private final Map<String, Integer> fieldPositionMap;
    private final List<String> fieldNames;

    /**
     *
     * @param fieldSchemas is now owned by HCatSchema. Any subsequent modifications
     * on fieldSchemas won't get reflected in HCatSchema.  Each fieldSchema's name
     * in the list must be unique, otherwise throws IllegalArgumentException.
     */
    public HCatSchema(final List<HCatFieldSchema> fieldSchemas) {
        this.fieldSchemas = new ArrayList<HCatFieldSchema>(fieldSchemas);
        int idx = 0;
        fieldPositionMap = new HashMap<String, Integer>();
        fieldNames = new ArrayList<String>();
        for (HCatFieldSchema field : fieldSchemas) {
            if (field == null)
                throw new IllegalArgumentException("Field cannot be null");

            String fieldName = field.getName();
            if (fieldPositionMap.containsKey(fieldName))
                throw new IllegalArgumentException("Field named " + fieldName +
                    " already exists");
            fieldPositionMap.put(fieldName, idx);
            fieldNames.add(fieldName);
            idx++;
        }
    }

    public void append(final HCatFieldSchema hfs) throws HCatException {
        if (hfs == null)
            throw new HCatException("Attempt to append null HCatFieldSchema in HCatSchema.");

        String fieldName = hfs.getName();
        if (fieldPositionMap.containsKey(fieldName))
            throw new HCatException("Attempt to append HCatFieldSchema with already " +
                "existing name: " + fieldName + ".");

        this.fieldSchemas.add(hfs);
        this.fieldNames.add(fieldName);
        this.fieldPositionMap.put(fieldName, this.size() - 1);
    }

    /**
     *  Users are not allowed to modify the list directly, since HCatSchema
     *  maintains internal state. Use append/remove to modify the schema.
     */
    public List<HCatFieldSchema> getFields() {
        return Collections.unmodifiableList(this.fieldSchemas);
    }

    /**
     * @param fieldName
     * @return the index of field named fieldName in Schema. If field is not
     * present, returns null.
     */
    public Integer getPosition(String fieldName) {
        return fieldPositionMap.get(fieldName);
    }

    public HCatFieldSchema get(String fieldName) throws HCatException {
        return get(getPosition(fieldName));
    }

    public List<String> getFieldNames() {
        return this.fieldNames;
    }

    public HCatFieldSchema get(int position) {
        return fieldSchemas.get(position);
    }

    public int size() {
        return fieldSchemas.size();
    }

    public void remove(final HCatFieldSchema hcatFieldSchema) throws HCatException {

        if (!fieldSchemas.contains(hcatFieldSchema)) {
            throw new HCatException("Attempt to delete a non-existent column from HCat Schema: " + hcatFieldSchema);
        }

        fieldSchemas.remove(hcatFieldSchema);
        fieldPositionMap.remove(hcatFieldSchema);
        fieldNames.remove(hcatFieldSchema.getName());
    }

    @Override
    public String toString() {
        boolean first = true;
        StringBuilder sb = new StringBuilder();
        for (HCatFieldSchema hfs : fieldSchemas) {
            if (!first) {
                sb.append(",");
            } else {
                first = false;
            }
            if (hfs.getName() != null) {
                sb.append(hfs.getName());
                sb.append(":");
            }
            sb.append(hfs.toString());
        }
        return sb.toString();
    }

    public String getSchemaAsTypeString() {
        boolean first = true;
        StringBuilder sb = new StringBuilder();
        for (HCatFieldSchema hfs : fieldSchemas) {
            if (!first) {
                sb.append(",");
            } else {
                first = false;
            }
            if (hfs.getName() != null) {
                sb.append(hfs.getName());
                sb.append(":");
            }
            sb.append(hfs.getTypeString());
        }
        return sb.toString();
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (!(obj instanceof HCatSchema)) {
            return false;
        }
        HCatSchema other = (HCatSchema) obj;
        if (!this.getFields().equals(other.getFields())) {
            return false;
        }
        return true;
    }

    @Override
    public int hashCode() {
        return toString().hashCode();
    }
}