Object Storage Service:Query files (Java SDK V1)

Usage notes

• In this topic, the public endpoint of the China (Hangzhou) region is used. To access OSS from other Alibaba Cloud services in the same region, use an internal endpoint. For details about supported regions and endpoints, see OSS regions and endpoints.

• In this topic, access credentials are obtained from environment variables. For more information about how to configure access credentials, see Configure access credentials.

• In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient instance by using custom domain names or Security Token Service (STS), see Configuration examples for common scenarios.

• To query files, you must have the oss:GetObject permission. For more information, see Attach a custom policy to a RAM user.

• Only objects in the CSV and JSON formats can be queried by using SelectObject.

Sample code

The following code provides an example of how to query CSV and JSON files.

import com.aliyun.oss.ClientBuilderConfiguration;
import com.aliyun.oss.common.comm.SignVersion;
import com.aliyun.oss.model.*;
import com.aliyun.oss.OSS;
import com.aliyun.oss.common.auth.*;
import com.aliyun.oss.OSSClientBuilder;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.InputStreamReader;

/**
 * Examples of create select object metadata and select object.
 *
 */
public class SelectObjectSample {
    // Set endpoint to the endpoint of the region where your bucket is located. For example, if your bucket is in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com.
    private static String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
    // Set bucketName to the name of your bucket, for example, examplebucket.
    private static String bucketName = "examplebucket";

    public static void main(String[] args) throws Exception {
      
      	// Obtain access credentials from environment variables. Before you run this code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are set.
        EnvironmentVariableCredentialsProvider credentialsProvider = CredentialsProviderFactory.newEnvironmentVariableCredentialsProvider();
        // Set region to the ID of the region where your bucket is located. For example, if your bucket is in the China (Hangzhou) region, set the region to cn-hangzhou.
        String region = "cn-hangzhou";

        // Create an OSSClient instance.
        // When the OSSClient instance is no longer needed, call the shutdown method to release its resources.
        ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration();
        clientBuilderConfiguration.setSignatureVersion(SignVersion.V4);        
        OSS ossClient = OSSClientBuilder.create()
        .endpoint(endpoint)
        .credentialsProvider(credentialsProvider)
        .clientConfiguration(clientBuilderConfiguration)
        .region(region)               
        .build();
        // Specify the full path of the object and query data from the file using a SELECT statement. The full path of the object cannot contain the bucket name.
        // Specify the full path of the CSV object.
        selectCsvSample("test.csv", ossClient);
        // Specify the full path of the JSON object.
        selectJsonSample("test.json", ossClient);
        ossClient.shutdown();
    }

    private static void selectCsvSample(String key, OSS ossClient) throws Exception {
        // Specify the content to upload.
        String content = "name,school,company,age\r\n" +
                "Lora Francis,School A,Staples Inc,27\r\n" +
                "Eleanor Little,School B,\"Conectiv, Inc\",43\r\n" +
                "Rosie Hughes,School C,Western Gas Resources Inc,44\r\n" +
                "Lawrence Ross,School D,MetLife Inc.,24";

        ossClient.putObject(bucketName, key, new ByteArrayInputStream(content.getBytes()));

        SelectObjectMetadata selectObjectMetadata = ossClient.createSelectObjectMetadata(
                new CreateSelectObjectMetadataRequest(bucketName, key)
                        .withInputSerialization(
                                new InputSerialization().withCsvInputFormat(
                                        // Specify the separator between records in the content, for example, \r\n.
                                        new CSVFormat().withHeaderInfo(CSVFormat.Header.Use).withRecordDelimiter("\r\n"))));
        System.out.println(selectObjectMetadata.getCsvObjectMetadata().getTotalLines());
        System.out.println(selectObjectMetadata.getCsvObjectMetadata().getSplits());

        SelectObjectRequest selectObjectRequest =
                new SelectObjectRequest(bucketName, key)
                        .withInputSerialization(
                                new InputSerialization().withCsvInputFormat(
                                        new CSVFormat().withHeaderInfo(CSVFormat.Header.Use).withRecordDelimiter("\r\n")))
                        .withOutputSerialization(new OutputSerialization().withCsvOutputFormat(new CSVFormat()));
        // Use a SELECT statement to query all records where the value in the fourth column is greater than 40.
        selectObjectRequest.setExpression("select * from ossobject where _4 > 40");
        OSSObject ossObject = ossClient.selectObject(selectObjectRequest);

        // Read the content.
        BufferedReader reader = new BufferedReader(new InputStreamReader(ossObject.getObjectContent()));
        while (true) {
            String line = reader.readLine();
            if (line == null) {
                break;
            }
            System.out.println(line);
        }
        reader.close();

        ossClient.deleteObject(bucketName, key);
    }

    private static void selectJsonSample(String key, OSS ossClient) throws Exception {
        // Specify the content to upload.
        final String content = "{\n" +
                "\t\"name\": \"Lora Francis\",\n" +
                "\t\"age\": 27,\n" +
                "\t\"company\": \"Staples Inc\"\n" +
                "}\n" +
                "{\n" +
                "\t\"name\": \"Eleanor Little\",\n" +
                "\t\"age\": 43,\n" +
                "\t\"company\": \"Conectiv, Inc\"\n" +
                "}\n" +
                "{\n" +
                "\t\"name\": \"Rosie Hughes\",\n" +
                "\t\"age\": 44,\n" +
                "\t\"company\": \"Western Gas Resources Inc\"\n" +
                "}\n" +
                "{\n" +
                "\t\"name\": \"Lawrence Ross\",\n" +
                "\t\"age\": 24,\n" +
                "\t\"company\": \"MetLife Inc.\"\n" +
                "}";

        ossClient.putObject(bucketName, key, new ByteArrayInputStream(content.getBytes()));

        SelectObjectRequest selectObjectRequest =
                new SelectObjectRequest(bucketName, key)
                        .withInputSerialization(new InputSerialization()
                                .withCompressionType(CompressionType.NONE)
                                .withJsonInputFormat(new JsonFormat().withJsonType(JsonType.LINES)))
                        .withOutputSerialization(new OutputSerialization()
                                .withCrcEnabled(true)
                                .withJsonOutputFormat(new JsonFormat()))
                        .withExpression("select * from ossobject as s where s.age > 40"); // Use a SELECT statement to query data from the file.

        OSSObject ossObject = ossClient.selectObject(selectObjectRequest);

        // Read the content.
        BufferedReader reader = new BufferedReader(new InputStreamReader(ossObject.getObjectContent()));
        while (true) {
            String line = reader.readLine();
            if (line == null) {
                break;
            }
            System.out.println(line);
        }
        reader.close();

        ossClient.deleteObject(bucketName, key);
    }
}

References

• For the complete sample code for querying files, see the GitHub example.

• For more information about the API operation for querying files, see SelectObject.