Java tutorial
/* * 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 gobblin.metrics.kafka; import java.io.IOException; import java.util.Properties; import java.util.concurrent.ExecutionException; import org.apache.avro.Schema; import org.apache.commons.httpclient.Header; import org.apache.commons.httpclient.HttpClient; import org.apache.commons.httpclient.HttpException; import org.apache.commons.httpclient.HttpStatus; import org.apache.commons.httpclient.methods.GetMethod; import org.apache.commons.httpclient.methods.PostMethod; import org.apache.commons.pool2.impl.GenericObjectPool; import org.apache.commons.pool2.impl.GenericObjectPoolConfig; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import com.google.common.base.Preconditions; import gobblin.configuration.ConfigurationKeys; import gobblin.kafka.schemareg.HttpClientFactory; import gobblin.util.AvroUtils; /** * An implementation of {@link KafkaSchemaRegistry}. * * @author Ziyang Liu */ public class KafkaAvroSchemaRegistry extends KafkaSchemaRegistry<String, Schema> { private static final Logger LOG = LoggerFactory.getLogger(KafkaAvroSchemaRegistry.class); private static final String GET_RESOURCE_BY_ID = "/id="; private static final String GET_RESOURCE_BY_TYPE = "/latest_with_type="; private static final String SCHEMA_ID_HEADER_NAME = "Location"; private static final String SCHEMA_ID_HEADER_PREFIX = "/id="; public static final int SCHEMA_ID_LENGTH_BYTE = 16; public static final byte MAGIC_BYTE = 0x0; private final GenericObjectPool<HttpClient> httpClientPool; private final String url; /** * @param properties properties should contain property "kafka.schema.registry.url", and optionally * "kafka.schema.registry.max.cache.size" (default = 1000) and * "kafka.schema.registry.cache.expire.after.write.min" (default = 10). */ public KafkaAvroSchemaRegistry(Properties props) { super(props); Preconditions.checkArgument(props.containsKey(KAFKA_SCHEMA_REGISTRY_URL), String.format("Property %s not provided.", KAFKA_SCHEMA_REGISTRY_URL)); this.url = props.getProperty(KAFKA_SCHEMA_REGISTRY_URL); int objPoolSize = Integer .parseInt(props.getProperty(ConfigurationKeys.KAFKA_SOURCE_WORK_UNITS_CREATION_THREADS, "" + ConfigurationKeys.KAFKA_SOURCE_WORK_UNITS_CREATION_DEFAULT_THREAD_COUNT)); LOG.info("Create HttpClient pool with size " + objPoolSize); GenericObjectPoolConfig config = new GenericObjectPoolConfig(); config.setMaxTotal(objPoolSize); config.setMaxIdle(objPoolSize); this.httpClientPool = new GenericObjectPool<>(new HttpClientFactory(), config); } /** * Returns the length of schema ids in this schema registry in bytes. */ public int getSchemaIdLengthByte() { return SCHEMA_ID_LENGTH_BYTE; } /** * Get schema from schema registry by key * * @param key Schema key * @return Schema with the corresponding key * @throws SchemaRegistryException if failed to retrieve schema. */ @Override public Schema getSchemaByKey(String key) throws SchemaRegistryException { try { return cachedSchemasByKeys.get(key); } catch (ExecutionException e) { throw new SchemaRegistryException(String.format("Schema with key %s cannot be retrieved", key), e); } } /** * Get the latest schema of a topic. * * @param topic topic name * @return the latest schema * @throws SchemaRegistryException if failed to retrieve schema. */ @Override public Schema getLatestSchemaByTopic(String topic) throws SchemaRegistryException { String schemaUrl = KafkaAvroSchemaRegistry.this.url + GET_RESOURCE_BY_TYPE + topic; LOG.debug("Fetching from URL : " + schemaUrl); GetMethod get = new GetMethod(schemaUrl); int statusCode; String schemaString; HttpClient httpClient = this.borrowClient(); try { statusCode = httpClient.executeMethod(get); schemaString = get.getResponseBodyAsString(); } catch (HttpException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } finally { get.releaseConnection(); this.httpClientPool.returnObject(httpClient); } if (statusCode != HttpStatus.SC_OK) { throw new SchemaRegistryException(String .format("Latest schema for topic %s cannot be retrieved. Status code = %d", topic, statusCode)); } Schema schema; try { schema = new Schema.Parser().parse(schemaString); } catch (Throwable t) { throw new SchemaRegistryException( String.format("Latest schema for topic %s cannot be retrieved", topic), t); } return schema; } private HttpClient borrowClient() throws SchemaRegistryException { try { return this.httpClientPool.borrowObject(); } catch (Exception e) { throw new SchemaRegistryException("Unable to borrow " + HttpClient.class.getSimpleName()); } } /** * Register a schema to the Kafka schema registry under the provided input name. This method will change the name * of the schema to the provided name. This is useful because certain services (like Gobblin kafka adaptor and * Camus) get the schema for a topic by querying for the latest schema with the topic name, requiring the topic * name and schema name to match for all topics. This method registers the schema to the schema registry in such a * way that any schema can be written to any topic. * * @param schema {@link org.apache.avro.Schema} to register. * @param overrideName Name of the schema when registerd to the schema registry. This name should match the name * of the topic where instances will be published. * @return schema ID of the registered schema. * @throws SchemaRegistryException if registration failed */ @Override public String register(Schema schema, String overrideName) throws SchemaRegistryException { return register(AvroUtils.switchName(schema, overrideName)); } /** * Register a schema to the Kafka schema registry * * @param schema * @return schema ID of the registered schema * @throws SchemaRegistryException if registration failed */ @Override public synchronized String register(Schema schema) throws SchemaRegistryException { LOG.info("Registering schema " + schema.toString()); PostMethod post = new PostMethod(url); post.addParameter("schema", schema.toString()); HttpClient httpClient = this.borrowClient(); try { LOG.debug("Loading: " + post.getURI()); int statusCode = httpClient.executeMethod(post); if (statusCode != HttpStatus.SC_CREATED) { throw new SchemaRegistryException("Error occurred while trying to register schema: " + statusCode); } String response; response = post.getResponseBodyAsString(); if (response != null) { LOG.info("Received response " + response); } String schemaKey; Header[] headers = post.getResponseHeaders(SCHEMA_ID_HEADER_NAME); if (headers.length != 1) { throw new SchemaRegistryException( "Error reading schema id returned by registerSchema call: headers.length = " + headers.length); } else if (!headers[0].getValue().startsWith(SCHEMA_ID_HEADER_PREFIX)) { throw new SchemaRegistryException( "Error parsing schema id returned by registerSchema call: header = " + headers[0].getValue()); } else { LOG.info("Registered schema successfully"); schemaKey = headers[0].getValue().substring(SCHEMA_ID_HEADER_PREFIX.length()); } return schemaKey; } catch (Throwable t) { throw new SchemaRegistryException(t); } finally { post.releaseConnection(); this.httpClientPool.returnObject(httpClient); } } /** * Fetch schema by key. */ @Override protected Schema fetchSchemaByKey(String key) throws SchemaRegistryException { String schemaUrl = KafkaAvroSchemaRegistry.this.url + GET_RESOURCE_BY_ID + key; GetMethod get = new GetMethod(schemaUrl); int statusCode; String schemaString; HttpClient httpClient = this.borrowClient(); try { statusCode = httpClient.executeMethod(get); schemaString = get.getResponseBodyAsString(); } catch (IOException e) { throw new SchemaRegistryException(e); } finally { get.releaseConnection(); this.httpClientPool.returnObject(httpClient); } if (statusCode != HttpStatus.SC_OK) { throw new SchemaRegistryException( String.format("Schema with key %s cannot be retrieved, statusCode = %d", key, statusCode)); } Schema schema; try { schema = new Schema.Parser().parse(schemaString); } catch (Throwable t) { throw new SchemaRegistryException(String.format("Schema with ID = %s cannot be parsed", key), t); } return schema; } }