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[examples] Improve the basic Java example
This improves the Java example in a bunch of ways: 1. Renames java-sample -> java-example. 2. Renames class to org.apache.kudu.examples.Example. 3. Adds licenses everywhere. 4. Rewrites the README, using adoc format. 5. Updates the pom, including syncing some plugin versions with java/pom and updating the version of the client the example uses. 6. Expands and improves the Example class: - Adds range partitioning with split rows. - Adds an alter table example. - Scans with a predicate and checks the results. Change-Id: I79ab5b0b2c30e8fd7c799857a0e3754b7618a580 Reviewed-on: http://gerrit.cloudera.org:8080/9852 Reviewed-by: Adar Dembo <[email protected]> Tested-by: Will Berkeley <[email protected]>
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| // 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. | ||
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| = Kudu Java client example README | ||
| :author: Kudu Team | ||
| :homepage: https://kudu.apache.org/ | ||
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| This is an example program that uses the synchronous Kudu Java client APIs to | ||
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| - Create a table | ||
| - Insert some rows | ||
| - Alter the table | ||
| - Scan some rows | ||
| - Delete the table | ||
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| To build and run, ensure maven is installed and from the java-example directory run: | ||
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| [source,bash] | ||
| ---- | ||
| $ mvn package | ||
| $ java -jar target/kudu-java-example-1.0-SNAPSHOT.jar | ||
| ---- | ||
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| By default, the example assumes the Kudu cluster has a single master running on | ||
| localhost with the default port 7051. To specify a different set of masters for | ||
| Kudu cluster, set the property `kuduMasters` to a CSV of the master addresses in | ||
| the form `host:port`, as shown: | ||
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| [source,bash] | ||
| ---- | ||
| $ java -DkuduMasters=master-0:7051,master-1:7051,master-2:7051 -jar target/kudu-java-example-1.0-SNAPSHOT.jar | ||
| ---- |
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examples/java/java-example/src/main/java/org/apache/kudu/examples/Example.java
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| // 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. | ||
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| package org.apache.kudu.examples; | ||
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| import java.util.ArrayList; | ||
| import java.util.List; | ||
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| import org.apache.kudu.ColumnSchema; | ||
| import org.apache.kudu.Schema; | ||
| import org.apache.kudu.Type; | ||
| import org.apache.kudu.client.AlterTableOptions; | ||
| import org.apache.kudu.client.CreateTableOptions; | ||
| import org.apache.kudu.client.Insert; | ||
| import org.apache.kudu.client.KuduClient; | ||
| import org.apache.kudu.client.KuduException; | ||
| import org.apache.kudu.client.KuduPredicate; | ||
| import org.apache.kudu.client.KuduPredicate.ComparisonOp; | ||
| import org.apache.kudu.client.KuduScanner; | ||
| import org.apache.kudu.client.KuduSession; | ||
| import org.apache.kudu.client.KuduTable; | ||
| import org.apache.kudu.client.PartialRow; | ||
| import org.apache.kudu.client.RowResult; | ||
| import org.apache.kudu.client.RowResultIterator; | ||
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| /* | ||
| * A simple example of using the synchronous Kudu Java client to | ||
| * - Create a table. | ||
| * - Insert rows. | ||
| * - Alter a table. | ||
| * - Scan rows. | ||
| * - Delete a table. | ||
| */ | ||
| public class Example { | ||
| private static final Double DEFAULT_DOUBLE = 12.345; | ||
| private static final String KUDU_MASTERS = System.getProperty("kuduMasters", "localhost:7051"); | ||
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| private static void createExampleTable(KuduClient client, String tableName) throws KuduException { | ||
| // Set up a simple schema. | ||
| List<ColumnSchema> columns = new ArrayList<>(2); | ||
| columns.add(new ColumnSchema.ColumnSchemaBuilder("key", Type.INT32) | ||
| .key(true) | ||
| .build()); | ||
| columns.add(new ColumnSchema.ColumnSchemaBuilder("value", Type.STRING).nullable(true) | ||
| .build()); | ||
| Schema schema = new Schema(columns); | ||
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| // Set up the partition schema, which distributes rows to different tablets by hash. | ||
| // Kudu also supports partitioning by key range. Hash and range partitioning can be combined. | ||
| // For more information, see http://kudu.apache.org/docs/schema_design.html. | ||
| CreateTableOptions cto = new CreateTableOptions(); | ||
| List<String> hashKeys = new ArrayList<>(1); | ||
| hashKeys.add("key"); | ||
| int numBuckets = 8; | ||
| cto.addHashPartitions(hashKeys, numBuckets); | ||
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| // Create the table. | ||
| client.createTable(tableName, schema, cto); | ||
| System.out.println("Created table " + tableName); | ||
| } | ||
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| private static void insertRows(KuduClient client, String tableName, int numRows) throws KuduException { | ||
| // Open the newly-created table and create a KuduSession. | ||
| KuduTable table = client.openTable(tableName); | ||
| KuduSession session = client.newSession(); | ||
| for (int i = 0; i < numRows; i++) { | ||
| Insert insert = table.newInsert(); | ||
| PartialRow row = insert.getRow(); | ||
| row.addInt("key", i); | ||
| // Make even-keyed row have a null 'value'. | ||
| if (i % 2 == 0) { | ||
| row.setNull("value"); | ||
| } else { | ||
| row.addString("value", "value " + i); | ||
| } | ||
| session.apply(insert); | ||
| } | ||
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| // Call session.close() to end the session and ensure the rows are | ||
| // flushed and errors are returned. | ||
| // You can also call session.flush() to do the same without ending the session. | ||
| // When flushing in AUTO_FLUSH_BACKGROUND mode (the default mode recommended | ||
| // for most workloads, you must check the pending errors as shown below, since | ||
| // write operations are flushed to Kudu in background threads. | ||
| session.close(); | ||
| if (session.countPendingErrors() != 0) { | ||
| System.out.println("errors inserting rows"); | ||
| org.apache.kudu.client.RowErrorsAndOverflowStatus roStatus = session.getPendingErrors(); | ||
| org.apache.kudu.client.RowError[] errs = roStatus.getRowErrors(); | ||
| int numErrs = Math.min(errs.length, 5); | ||
| System.out.println("there were errors inserting rows to Kudu"); | ||
| System.out.println("the first few errors follow:"); | ||
| for (int i = 0; i < numErrs; i++) { | ||
| System.out.println(errs[i]); | ||
| } | ||
| if (roStatus.isOverflowed()) { | ||
| System.out.println("error buffer overflowed: some errors were discarded"); | ||
| } | ||
| throw new RuntimeException("error inserting rows to Kudu"); | ||
| } | ||
| System.out.println("Inserted " + numRows + " rows"); | ||
| } | ||
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| private static void scanTableAndCheckResults(KuduClient client, String tableName, int numRows) throws KuduException { | ||
| KuduTable table = client.openTable(tableName); | ||
| Schema schema = table.getSchema(); | ||
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| // Scan with a predicate on the 'key' column, returning the 'value' and "added" columns. | ||
| List<String> projectColumns = new ArrayList<>(2); | ||
| projectColumns.add("key"); | ||
| projectColumns.add("value"); | ||
| projectColumns.add("added"); | ||
| int lowerBound = 0; | ||
| KuduPredicate lowerPred = KuduPredicate.newComparisonPredicate( | ||
| schema.getColumn("key"), | ||
| ComparisonOp.GREATER_EQUAL, | ||
| lowerBound); | ||
| int upperBound = numRows / 2; | ||
| KuduPredicate upperPred = KuduPredicate.newComparisonPredicate( | ||
| schema.getColumn("key"), | ||
| ComparisonOp.LESS, | ||
| upperBound); | ||
| KuduScanner scanner = client.newScannerBuilder(table) | ||
| .setProjectedColumnNames(projectColumns) | ||
| .addPredicate(lowerPred) | ||
| .addPredicate(upperPred) | ||
| .build(); | ||
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| // Check the correct number of values and null values are returned, and | ||
| // that the default value was set for the new column on each row. | ||
| // Note: scanning a hash-partitioned table will not return results in primary key order. | ||
| int resultCount = 0; | ||
| int nullCount = 0; | ||
| while (scanner.hasMoreRows()) { | ||
| RowResultIterator results = scanner.nextRows(); | ||
| while (results.hasNext()) { | ||
| RowResult result = results.next(); | ||
| if (result.isNull("value")) { | ||
| nullCount++; | ||
| } | ||
| double added = result.getDouble("added"); | ||
| if (added != DEFAULT_DOUBLE) { | ||
| throw new RuntimeException("expected added=" + DEFAULT_DOUBLE + | ||
| " but got added= " + added); | ||
| } | ||
| resultCount++; | ||
| } | ||
| } | ||
| int expectedResultCount = upperBound - lowerBound; | ||
| if (resultCount != expectedResultCount) { | ||
| throw new RuntimeException("scan error: expected " + expectedResultCount + | ||
| " results but got " + resultCount + " results"); | ||
| } | ||
| int expectedNullCount = expectedResultCount / 2 + (numRows % 2 == 0 ? 1 : 0); | ||
| if (nullCount != expectedNullCount) { | ||
| throw new RuntimeException("scan error: expected " + expectedNullCount + | ||
| " rows with value=null but found " + nullCount); | ||
| } | ||
| System.out.println("Scanned some rows and checked the results"); | ||
| } | ||
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| public static void main(String[] args) { | ||
| System.out.println("-----------------------------------------------"); | ||
| System.out.println("Will try to connect to Kudu master(s) at " + KUDU_MASTERS); | ||
| System.out.println("Run with -DkuduMasters=master-0:port,master-1:port,... to override."); | ||
| System.out.println("-----------------------------------------------"); | ||
| String tableName = "java_example-" + System.currentTimeMillis(); | ||
| KuduClient client = new KuduClient.KuduClientBuilder(KUDU_MASTERS).build(); | ||
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| try { | ||
| createExampleTable(client, tableName); | ||
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| int numRows = 150; | ||
| insertRows(client, tableName, numRows); | ||
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| // Alter the table, adding a column with a default value. | ||
| // Note: after altering the table, the table needs to be re-opened. | ||
| AlterTableOptions ato = new AlterTableOptions(); | ||
| ato.addColumn("added", org.apache.kudu.Type.DOUBLE, DEFAULT_DOUBLE); | ||
| client.alterTable(tableName, ato); | ||
| System.out.println("Altered the table"); | ||
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| scanTableAndCheckResults(client, tableName, numRows); | ||
| } catch (Exception e) { | ||
| e.printStackTrace(); | ||
| } finally { | ||
| try { | ||
| client.deleteTable(tableName); | ||
| System.out.println("Deleted the table"); | ||
| } catch (Exception e) { | ||
| e.printStackTrace(); | ||
| } finally { | ||
| try { | ||
| client.shutdown(); | ||
| } catch (Exception e) { | ||
| e.printStackTrace(); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } |
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