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Java ​

GreptimeDB uses different client libraries for writing and querying data. You can choose the client library that best suits your needs.

Write data ​

GreptimeDB provides an ingester library to help you write data. It utilizes the gRPC protocol, which supports schemaless writing and eliminates the need to create tables before writing data. For more information, refer to Automatic Schema Generation.

The Java ingester SDK provided by GreptimeDB is a lightweight library with the following features:

  • SPI-based extensible network transport layer, which provides the default implementation using the gRPC framework.
  • Non-blocking, purely asynchronous API that is easy to use.
  • Automatic collection of various performance metrics by default. You can then configure and write them to local files.
  • Ability to take in-memory snapshots of critical objects, configure them, and write them to local files. This is helpful for troubleshooting complex issues.

Installation ​

  1. Install the Java Development Kit(JDK)

Make sure that your system has JDK 8 or later installed. For more information on how to check your version of Java and install the JDK, see the Oracle Overview of JDK Installation documentation

  1. Add GreptiemDB Java SDK as a Dependency

If you are using Maven, add the following to your pom.xml dependencies list:

xml
<dependency>
    <groupId>io.greptime</groupId>
    <artifactId>ingester-all</artifactId>
    <version>${latest_version}</version>
</dependency>
<dependency>
    <groupId>io.greptime</groupId>
    <artifactId>ingester-all</artifactId>
    <version>${latest_version}</version>
</dependency>

The latest version can be viewed here.

After configuring your dependencies, make sure they are available to your project. This may require refreshing the project in your IDE or running the dependency manager.

Connect to database ​

Username and password are always required to connect to GreptimeDB. For how to set authentication to GreptimeDB, see Authentication. Here we set the username and password when using the library to connect to GreptimeDB.

The following code demonstrates how to connect to GreptimeDB with the simplest configuration. For customizing the connection options, please refer to API Documentation. Please pay attention to the accompanying comments for each option, as they provide detailed explanations of their respective roles.

java
// GreptimeDB has a default database named "public" in the default catalog "greptime",
// we can use it as the test database
String database = "public";
// By default, GreptimeDB listens on port 4001 using the gRPC protocol.
// We can provide multiple endpoints that point to the same GreptimeDB cluster.
// The client will make calls to these endpoints based on a load balancing strategy.
String[] endpoints = {"127.0.0.1:4001"};
// Sets authentication information.
AuthInfo authInfo = new AuthInfo("username", "password");
GreptimeOptions opts = GreptimeOptions.newBuilder(endpoints, database)
        // If the database does not require authentication, we can use AuthInfo.noAuthorization() as the parameter.
        .authInfo(authInfo)
        // Enable secure connection if your server is secured by TLS
        //.tlsOptions(new TlsOptions())
        // A good start ^_^
        .build();

GreptimeDB client = GreptimeDB.create(opts);
// GreptimeDB has a default database named "public" in the default catalog "greptime",
// we can use it as the test database
String database = "public";
// By default, GreptimeDB listens on port 4001 using the gRPC protocol.
// We can provide multiple endpoints that point to the same GreptimeDB cluster.
// The client will make calls to these endpoints based on a load balancing strategy.
String[] endpoints = {"127.0.0.1:4001"};
// Sets authentication information.
AuthInfo authInfo = new AuthInfo("username", "password");
GreptimeOptions opts = GreptimeOptions.newBuilder(endpoints, database)
        // If the database does not require authentication, we can use AuthInfo.noAuthorization() as the parameter.
        .authInfo(authInfo)
        // Enable secure connection if your server is secured by TLS
        //.tlsOptions(new TlsOptions())
        // A good start ^_^
        .build();

GreptimeDB client = GreptimeDB.create(opts);

For customizing the connection options, please refer to API Documentation.

Data model ​

Each row item in a table consists of three types of columns: Tag, Timestamp, and Field. For more information, see Data Model. The types of column values could be String, Float, Int, Timestamp, etc. For more information, see Data Types.

Low-level API ​

The GreptimeDB low-level API provides a straightforward method to write data to GreptimeDB by adding rows to the table object with a predefined schema.

Create row objects ​

This following code snippet begins by constructing a table named cpu_metric, which includes columns host, cpu_user, cpu_sys, and ts. Subsequently, it inserts a single row into the table.

The table consists of three types of columns:

  • Tag: The host column, with values of type String.
  • Field: The cpu_user and cpu_sys columns, with values of type Float.
  • Timestamp: The ts column, with values of type Timestamp.
java
// Construct the table schema for CPU metrics
TableSchema cpuMetricSchema = TableSchema.newBuilder("cpu_metric")
        .addTag("host", DataType.String) // Identifier for the host
        .addTimestamp("ts", DataType.TimestampMillisecond) // Timestamp in milliseconds
        .addField("cpu_user", DataType.Float64) // CPU usage by user processes
        .addField("cpu_sys", DataType.Float64) // CPU usage by system processes
        .build();

// Create the table from the defined schema
Table cpuMetric = Table.from(cpuMetricSchema);

// Example data for a single row
String host = "127.0.0.1"; // Host identifier
long ts = System.currentTimeMillis(); // Current timestamp
double cpuUser = 0.1; // CPU usage by user processes (in percentage)
double cpuSys = 0.12; // CPU usage by system processes (in percentage)

// Insert the row into the table
// NOTE: The arguments must be in the same order as the columns in the defined schema: host, ts, cpu_user, cpu_sys
cpuMetric.addRow(host, ts, cpuUser, cpuSys);
// Construct the table schema for CPU metrics
TableSchema cpuMetricSchema = TableSchema.newBuilder("cpu_metric")
        .addTag("host", DataType.String) // Identifier for the host
        .addTimestamp("ts", DataType.TimestampMillisecond) // Timestamp in milliseconds
        .addField("cpu_user", DataType.Float64) // CPU usage by user processes
        .addField("cpu_sys", DataType.Float64) // CPU usage by system processes
        .build();

// Create the table from the defined schema
Table cpuMetric = Table.from(cpuMetricSchema);

// Example data for a single row
String host = "127.0.0.1"; // Host identifier
long ts = System.currentTimeMillis(); // Current timestamp
double cpuUser = 0.1; // CPU usage by user processes (in percentage)
double cpuSys = 0.12; // CPU usage by system processes (in percentage)

// Insert the row into the table
// NOTE: The arguments must be in the same order as the columns in the defined schema: host, ts, cpu_user, cpu_sys
cpuMetric.addRow(host, ts, cpuUser, cpuSys);

To improve the efficiency of writing data, you can create multiple rows at once to write to GreptimeDB.

java
// Creates schemas
TableSchema cpuMetricSchema = TableSchema.newBuilder("cpu_metric")
        .addTag("host", DataType.String)
        .addTimestamp("ts", DataType.TimestampMillisecond)
        .addField("cpu_user", DataType.Float64)
        .addField("cpu_sys", DataType.Float64)
        .build();

TableSchema memMetricSchema = TableSchema.newBuilder("mem_metric")
        .addTag("host", DataType.String)
        .addTimestamp("ts", DataType.TimestampMillisecond)
        .addField("mem_usage", DataType.Float64)
        .build();

Table cpuMetric = Table.from(cpuMetricSchema);
Table memMetric = Table.from(memMetricSchema);

// Adds row data items
for (int i = 0; i < 10; i++) {
    String host = "127.0.0." + i;
    long ts = System.currentTimeMillis();
    double cpuUser = i + 0.1;
    double cpuSys = i + 0.12;
    cpuMetric.addRow(host, ts, cpuUser, cpuSys);
}

for (int i = 0; i < 10; i++) {
    String host = "127.0.0." + i;
    long ts = System.currentTimeMillis();
    double memUsage = i + 0.2;
    memMetric.addRow(host, ts, memUsage);
}
// Creates schemas
TableSchema cpuMetricSchema = TableSchema.newBuilder("cpu_metric")
        .addTag("host", DataType.String)
        .addTimestamp("ts", DataType.TimestampMillisecond)
        .addField("cpu_user", DataType.Float64)
        .addField("cpu_sys", DataType.Float64)
        .build();

TableSchema memMetricSchema = TableSchema.newBuilder("mem_metric")
        .addTag("host", DataType.String)
        .addTimestamp("ts", DataType.TimestampMillisecond)
        .addField("mem_usage", DataType.Float64)
        .build();

Table cpuMetric = Table.from(cpuMetricSchema);
Table memMetric = Table.from(memMetricSchema);

// Adds row data items
for (int i = 0; i < 10; i++) {
    String host = "127.0.0." + i;
    long ts = System.currentTimeMillis();
    double cpuUser = i + 0.1;
    double cpuSys = i + 0.12;
    cpuMetric.addRow(host, ts, cpuUser, cpuSys);
}

for (int i = 0; i < 10; i++) {
    String host = "127.0.0." + i;
    long ts = System.currentTimeMillis();
    double memUsage = i + 0.2;
    memMetric.addRow(host, ts, memUsage);
}

Insert data ​

The following example shows how to insert rows to tables in GreptimeDB.

java
// Saves data

// For performance reasons, the SDK is designed to be purely asynchronous.
// The return value is a future object. If you want to immediately obtain
// the result, you can call `future.get()`.
CompletableFuture<Result<WriteOk, Err>> future = greptimeDB.write(cpuMetric, memMetric);

Result<WriteOk, Err> result = future.get();

if (result.isOk()) {
    LOG.info("Write result: {}", result.getOk());
} else {
    LOG.error("Failed to write: {}", result.getErr());
}
// Saves data

// For performance reasons, the SDK is designed to be purely asynchronous.
// The return value is a future object. If you want to immediately obtain
// the result, you can call `future.get()`.
CompletableFuture<Result<WriteOk, Err>> future = greptimeDB.write(cpuMetric, memMetric);

Result<WriteOk, Err> result = future.get();

if (result.isOk()) {
    LOG.info("Write result: {}", result.getOk());
} else {
    LOG.error("Failed to write: {}", result.getErr());
}

Streaming insert ​

Streaming insert is useful when you want to insert a large amount of data such as importing historical data.

java
StreamWriter<Table, WriteOk> writer = greptimeDB.streamWriter();

// write data into stream
writer.write(cpuMetric);
writer.write(memMetric);

// You can perform operations on the stream, such as deleting the first 5 rows.
writer.write(cpuMetric.subRange(0, 5), WriteOp.Delete);
StreamWriter<Table, WriteOk> writer = greptimeDB.streamWriter();

// write data into stream
writer.write(cpuMetric);
writer.write(memMetric);

// You can perform operations on the stream, such as deleting the first 5 rows.
writer.write(cpuMetric.subRange(0, 5), WriteOp.Delete);

Close the stream writing after all data has been written. In general, you do not need to close the stream writing when continuously writing data.

java
// complete the stream
CompletableFuture<WriteOk> future = writer.completed();
WriteOk result = future.get();
LOG.info("Write result: {}", result);
// complete the stream
CompletableFuture<WriteOk> future = writer.completed();
WriteOk result = future.get();
LOG.info("Write result: {}", result);

Update data ​

Please refer to update data for the updating mechanism. In the following code, we first save a row and then use the same tag and time index to identify the row for updating.

java
Table cpuMetric = Table.from(myMetricCpuSchema);
// insert a row data
long ts = 1703832681000L;
cpuMetric.addRow("host1", ts, 0.23, 0.12);
Result<WriteOk, Err> putResult = greptimeDB.write(cpuMetric).get();

// update the row data
Table newCpuMetric = Table.from(myMetricCpuSchema);
// The same tag `host1`
// The same time index `1703832681000`
// The new value: cpu_user = `0.80`, cpu_sys = `0.11`
long ts = 1703832681000L;
myMetricCpuSchema.addRow("host1", ts, 0.80, 0.11);

// overwrite the existing data
CompletableFuture<Result<WriteOk, Err>> future = greptimeDB.write(myMetricCpuSchema);
Result<WriteOk, Err> result = future.get();
Table cpuMetric = Table.from(myMetricCpuSchema);
// insert a row data
long ts = 1703832681000L;
cpuMetric.addRow("host1", ts, 0.23, 0.12);
Result<WriteOk, Err> putResult = greptimeDB.write(cpuMetric).get();

// update the row data
Table newCpuMetric = Table.from(myMetricCpuSchema);
// The same tag `host1`
// The same time index `1703832681000`
// The new value: cpu_user = `0.80`, cpu_sys = `0.11`
long ts = 1703832681000L;
myMetricCpuSchema.addRow("host1", ts, 0.80, 0.11);

// overwrite the existing data
CompletableFuture<Result<WriteOk, Err>> future = greptimeDB.write(myMetricCpuSchema);
Result<WriteOk, Err> result = future.get();

High-level API ​

The high-level API uses an ORM style object to write data to GreptimeDB. It allows you to create, insert, and update data in a more object-oriented way, providing developers with a friendlier experience. However, it is not as efficient as the low-level API. This is because the ORM style object may consume more resources and time when converting the objects.

Create row objects ​

GreptimeDB Java Ingester SDK allows us to use basic POJO objects for writing. This approach requires the use of Greptime's own annotations, but they are easy to use.

java
@Metric(name = "cpu_metric")
public class Cpu {
    @Column(name = "host", tag = true, dataType = DataType.String)
    private String host;

    @Column(name = "ts", timestamp = true, dataType = DataType.TimestampMillisecond)
    private long ts;

    @Column(name = "cpu_user", dataType = DataType.Float64)
    private double cpuUser;
    @Column(name = "cpu_sys", dataType = DataType.Float64)
    private double cpuSys;

    // getters and setters
    // ...
}

@Metric(name = "mem_metric")
public class Memory {
    @Column(name = "host", tag = true, dataType = DataType.String)
    private String host;

    @Column(name = "ts", timestamp = true, dataType = DataType.TimestampMillisecond)
    private long ts;

    @Column(name = "mem_usage", dataType = DataType.Float64)
    private double memUsage;
    // getters and setters
    // ...
}

// Add rows
List<Cpu> cpus = new ArrayList<>();
for (int i = 0; i < 10; i++) {
    Cpu c = new Cpu();
    c.setHost("127.0.0." + i);
    c.setTs(System.currentTimeMillis());
    c.setCpuUser(i + 0.1);
    c.setCpuSys(i + 0.12);
    cpus.add(c);
}

List<Memory> memories = new ArrayList<>();
for (int i = 0; i < 10; i++) {
    Memory m = new Memory();
    m.setHost("127.0.0." + i);
    m.setTs(System.currentTimeMillis());
    m.setMemUsage(i + 0.2);
    memories.add(m);
}
@Metric(name = "cpu_metric")
public class Cpu {
    @Column(name = "host", tag = true, dataType = DataType.String)
    private String host;

    @Column(name = "ts", timestamp = true, dataType = DataType.TimestampMillisecond)
    private long ts;

    @Column(name = "cpu_user", dataType = DataType.Float64)
    private double cpuUser;
    @Column(name = "cpu_sys", dataType = DataType.Float64)
    private double cpuSys;

    // getters and setters
    // ...
}

@Metric(name = "mem_metric")
public class Memory {
    @Column(name = "host", tag = true, dataType = DataType.String)
    private String host;

    @Column(name = "ts", timestamp = true, dataType = DataType.TimestampMillisecond)
    private long ts;

    @Column(name = "mem_usage", dataType = DataType.Float64)
    private double memUsage;
    // getters and setters
    // ...
}

// Add rows
List<Cpu> cpus = new ArrayList<>();
for (int i = 0; i < 10; i++) {
    Cpu c = new Cpu();
    c.setHost("127.0.0." + i);
    c.setTs(System.currentTimeMillis());
    c.setCpuUser(i + 0.1);
    c.setCpuSys(i + 0.12);
    cpus.add(c);
}

List<Memory> memories = new ArrayList<>();
for (int i = 0; i < 10; i++) {
    Memory m = new Memory();
    m.setHost("127.0.0." + i);
    m.setTs(System.currentTimeMillis());
    m.setMemUsage(i + 0.2);
    memories.add(m);
}

Insert data ​

Write data with POJO objects:

java
// Saves data

CompletableFuture<Result<WriteOk, Err>> puts = greptimeDB.writeObjects(cpus, memories);

Result<WriteOk, Err> result = puts.get();

if (result.isOk()) {
    LOG.info("Write result: {}", result.getOk());
} else {
    LOG.error("Failed to write: {}", result.getErr());
}
// Saves data

CompletableFuture<Result<WriteOk, Err>> puts = greptimeDB.writeObjects(cpus, memories);

Result<WriteOk, Err> result = puts.get();

if (result.isOk()) {
    LOG.info("Write result: {}", result.getOk());
} else {
    LOG.error("Failed to write: {}", result.getErr());
}

Streaming insert ​

Streaming insert is useful when you want to insert a large amount of data such as importing historical data.

java
StreamWriter<List<?>, WriteOk> writer = greptimeDB.objectsStreamWriter();

// write data into stream
writer.write(cpus);
writer.write(memories);

// You can perform operations on the stream, such as deleting the first 5 rows.
writer.write(cpus.subList(0, 5), WriteOp.Delete);
StreamWriter<List<?>, WriteOk> writer = greptimeDB.objectsStreamWriter();

// write data into stream
writer.write(cpus);
writer.write(memories);

// You can perform operations on the stream, such as deleting the first 5 rows.
writer.write(cpus.subList(0, 5), WriteOp.Delete);

Close the stream writing after all data has been written. In general, you do not need to close the stream writing when continuously writing data.

java
// complete the stream
CompletableFuture<WriteOk> future = writer.completed();
WriteOk result = future.get();
LOG.info("Write result: {}", result);
// complete the stream
CompletableFuture<WriteOk> future = writer.completed();
WriteOk result = future.get();
LOG.info("Write result: {}", result);

Update data ​

Please refer to update data for the updating mechanism. In the following code, we first save a row and then use the same tag and time index to identify the row for updating.

java
Cpu cpu = new Cpu();
cpu.setHost("host1");
cpu.setTs(1703832681000L);
cpu.setCpuUser(0.23);
cpu.setCpuSys(0.12);

// insert a row data
Result<WriteOk, Err> putResult = greptimeDB.writeObjects(cpu).get();

// update the row data
Cpu newCpu = new Cpu();
// The same tag `host1`
newCpu.setHost("host1");
// The same time index `1703832681000`
newCpu.setTs(1703832681000L);
// The new value: cpu_user = `0.80`, cpu_sys = `0.11`
cpu.setCpuUser(0.80);
cpu.setCpuSys(0.11);

// overwrite the existing data
Result<WriteOk, Err> updateResult = greptimeDB.writeObjects(newCpu).get();
Cpu cpu = new Cpu();
cpu.setHost("host1");
cpu.setTs(1703832681000L);
cpu.setCpuUser(0.23);
cpu.setCpuSys(0.12);

// insert a row data
Result<WriteOk, Err> putResult = greptimeDB.writeObjects(cpu).get();

// update the row data
Cpu newCpu = new Cpu();
// The same tag `host1`
newCpu.setHost("host1");
// The same time index `1703832681000`
newCpu.setTs(1703832681000L);
// The new value: cpu_user = `0.80`, cpu_sys = `0.11`
cpu.setCpuUser(0.80);
cpu.setCpuSys(0.11);

// overwrite the existing data
Result<WriteOk, Err> updateResult = greptimeDB.writeObjects(newCpu).get();

More examples ​

For fully runnable code snippets and the complete code of the demo, please refer to the Examples.

Debug logs ​

The ingester SDK provides metrics and logs for debugging. Please refer to Metrics & Display and Magic Tools to learn how to enable or disable the logs.

Ingester library reference ​

Query data ​

GreptimeDB uses SQL as the main query language and is compatible with MySQL and PostgreSQL. Therefore, we recommend using mature SQL drivers to query data.

Java database connectivity (JDBC) is the JavaSoft specification of a standard application programming interface (API) that allows Java programs to access database management systems.

Many databases, such as MySQL or PostgreSQL, have implemented their own drivers based on the JDBC API. Since GreptimeDB supports mutiple protocols, we use MySQL as an example to demonstrate how to use JDBC. If you want to use other protocols, just replace the MySQL driver with the corresponding driver.

Installation ​

If you are using Maven, add the following to your pom.xml dependencies list:

xml
<!-- MySQL usage dependency -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.33</version>
</dependency>
<!-- MySQL usage dependency -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.33</version>
</dependency>

Connect to database ​

The following example shows how to connect to GreptimeDB:

Here we will use MySQL as an example to demonstrate how to connect to GreptimeDB.

java

public static Connection getConnection() throws IOException, ClassNotFoundException, SQLException {
    Properties prop = new Properties();
    prop.load(QueryJDBC.class.getResourceAsStream("/db-connection.properties"));

    String dbName = (String) prop.get("db.database-driver");

    String dbConnUrl = (String) prop.get("db.url");
    String dbUserName = (String) prop.get("db.username");
    String dbPassword = (String) prop.get("db.password");

    Class.forName(dbName);
    Connection dbConn = DriverManager.getConnection(dbConnUrl, dbUserName, dbPassword);

    return Objects.requireNonNull(dbConn, "Failed to make connection!");
}

public static Connection getConnection() throws IOException, ClassNotFoundException, SQLException {
    Properties prop = new Properties();
    prop.load(QueryJDBC.class.getResourceAsStream("/db-connection.properties"));

    String dbName = (String) prop.get("db.database-driver");

    String dbConnUrl = (String) prop.get("db.url");
    String dbUserName = (String) prop.get("db.username");
    String dbPassword = (String) prop.get("db.password");

    Class.forName(dbName);
    Connection dbConn = DriverManager.getConnection(dbConnUrl, dbUserName, dbPassword);

    return Objects.requireNonNull(dbConn, "Failed to make connection!");
}

You need a properties file to store the DB connection information. Place it in the Resources directory and name it db-connection.properties. The file content is as follows:

txt
# DataSource
db.database-driver=com.mysql.cj.jdbc.Driver
db.url=jdbc:mysql://localhost:4002/public
db.username=
db.password=
# DataSource
db.database-driver=com.mysql.cj.jdbc.Driver
db.url=jdbc:mysql://localhost:4002/public
db.username=
db.password=

Or you can just get the file from here.

Raw SQL ​

We recommend you using raw SQL to experience the full features of GreptimeDB. The following example shows how to use raw SQL to query data.

java
try (Connection conn = getConnection()) {
    Statement statement = conn.createStatement();

    // DESC table;
    ResultSet rs = statement.executeQuery("DESC cpu_metric");
    LOG.info("Column | Type | Key | Null | Default | Semantic Type ");
    while (rs.next()) {
        LOG.info("{} | {} | {} | {} | {} | {}",
                rs.getString(1),
                rs.getString(2),
                rs.getString(3),
                rs.getString(4),
                rs.getString(5),
                rs.getString(6));
    }

    // SELECT COUNT(*) FROM cpu_metric;
    rs = statement.executeQuery("SELECT COUNT(*) FROM cpu_metric");
    while (rs.next()) {
        LOG.info("Count: {}", rs.getInt(1));
    }

    // SELECT * FROM cpu_metric ORDER BY ts DESC LIMIT 5;
    rs = statement.executeQuery("SELECT * FROM cpu_metric ORDER BY ts DESC LIMIT 5");
    LOG.info("host | ts | cpu_user | cpu_sys");
    while (rs.next()) {
        LOG.info("{} | {} | {} | {}",
                rs.getString("host"),
                rs.getTimestamp("ts"),
                rs.getDouble("cpu_user"),
                rs.getDouble("cpu_sys"));
    }
}
try (Connection conn = getConnection()) {
    Statement statement = conn.createStatement();

    // DESC table;
    ResultSet rs = statement.executeQuery("DESC cpu_metric");
    LOG.info("Column | Type | Key | Null | Default | Semantic Type ");
    while (rs.next()) {
        LOG.info("{} | {} | {} | {} | {} | {}",
                rs.getString(1),
                rs.getString(2),
                rs.getString(3),
                rs.getString(4),
                rs.getString(5),
                rs.getString(6));
    }

    // SELECT COUNT(*) FROM cpu_metric;
    rs = statement.executeQuery("SELECT COUNT(*) FROM cpu_metric");
    while (rs.next()) {
        LOG.info("Count: {}", rs.getInt(1));
    }

    // SELECT * FROM cpu_metric ORDER BY ts DESC LIMIT 5;
    rs = statement.executeQuery("SELECT * FROM cpu_metric ORDER BY ts DESC LIMIT 5");
    LOG.info("host | ts | cpu_user | cpu_sys");
    while (rs.next()) {
        LOG.info("{} | {} | {} | {}",
                rs.getString("host"),
                rs.getTimestamp("ts"),
                rs.getDouble("cpu_user"),
                rs.getDouble("cpu_sys"));
    }
}

For the complete code of the demo, please refer to here.

Query library reference ​

For more information about how to use the query library, please see the documentation of the corresponding library:

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