harmony 鸿蒙@ohos.hilog (HiLog)

2022-08-09
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@ohos.hilog (HiLog)

The HiLog subsystem allows your applications or services to output logs based on the specified type, level, and format string. Such logs help you learn the running status of applications and better debug programs.

NOTE

The initial APIs of this module are supported since API version 7. Newly added APIs will be marked with a superscript to indicate their earliest API version.

Modules to Import

import hilog from '@ohos.hilog';

hilog.isLoggable

isLoggable(domain: number, tag: string, level: LogLevel) : boolean

Checks whether logs are printable based on the specified service domain, log tag, and log level.

System capability: SystemCapability.HiviewDFX.HiLog

Parameters

Name	Type	Mandatory	Description
domain	number	Yes	Service domain of logs. The value ranges from 0x0 to 0xFFFF. You can define the value as required.
tag	string	Yes	Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.
level	LogLevel	Yes	Log level.

Return value

Type	Description
boolean	Returns true logs are printable based on the specified service domain, log tag, and log level; returns false otherwise.

Example

hilog.isLoggable(0x0001, "testTag", hilog.LogLevel.INFO);

LogLevel

Log level.

System capability: SystemCapability.HiviewDFX.HiLog

Name	Value	Description
DEBUG	3	Log level used to record more detailed process information than INFO logs to help developers analyze service processes and locate faults.
INFO	4	Log level used to record key service process nodes and exceptions that occur during service running, for example, no network signal or login failure. These logs should be recorded by the dominant module in the service to avoid repeated logging conducted by multiple invoked modules or low-level functions.
WARN	5	Log level used to record severe, unexpected faults that have little impact on users and can be rectified by the programs themselves or through simple operations.
ERROR	6	Log level used to record program or functional errors that affect the normal running or use of the functionality and can be fixed at a high cost, for example, by resetting data.
FATAL	7	Log level used to record program or functionality crashes that cannot be rectified.

hilog.debug

debug(domain: number, tag: string, format: string, …args: any[]) : void

Prints DEBUG logs.

DEBUG logs are not recorded in official versions by default. They are available in debug versions or in official versions with the debug function enabled.

System capability: SystemCapability.HiviewDFX.HiLog

Parameters

Name	Type	Mandatory	Description
domain	number	Yes	Service domain of logs. The value ranges from 0x0 to 0xFFFF. You can define the value as required.
tag	string	Yes	Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.
format	string	Yes	Format string used to output logs in a specified format. It can contain several elements, where the parameter type and privacy identifier are mandatory. Parameters labeled {public} are public data and are displayed in plaintext; parameters labeled {private} (default value) are private data and are filtered by <private>.
args	any[]	Yes	Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.

Example

This example is used to output a DEBUG log with the format string being "%{public}s World %{private}d". The variable %{public}s is a plaintext string, and the variable %{private}d is a private integer.

hilog.debug(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3);

If "hello" is filled in %{public}s and 3 in %{private}d, the output log is as follows:

08-05 12:21:47.579  2695-2703/com.example.myapplication D 00001/testTag: hello World <private>

hilog.info

info(domain: number, tag: string, format: string, …args: any[]) : void

Prints INFO logs.

System capability: SystemCapability.HiviewDFX.HiLog

Parameters

Name	Type	Mandatory	Description
domain	number	Yes	Service domain of logs. The value ranges from 0x0 to 0xFFFF. You can define the value as required.
tag	string	Yes	Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.
format	string	Yes	Format string used to output logs in a specified format. It can contain several elements, where the parameter type and privacy identifier are mandatory. Parameters labeled {public} are public data and are displayed in plaintext; parameters labeled {private} (default value) are private data and are filtered by <private>.
args	any[]	Yes	Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.

Example

This example is used to output an INFO log with the format string being "%{public}s World %{private}d". The variable %{public}s is a plaintext string, and the variable %{private}d is a private integer.

hilog.info(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3);

If "hello" is filled in %{public}s and 3 in %{private}d, the output log is as follows:

08-05 12:21:47.579  2695-2703/com.example.myapplication I 00001/testTag: hello World <private>

hilog.warn

warn(domain: number, tag: string, format: string, …args: any[]) : void

Prints WARN logs.

System capability: SystemCapability.HiviewDFX.HiLog

Parameters

Name	Type	Mandatory	Description
domain	number	Yes	Service domain of logs. The value ranges from 0x0 to 0xFFFF. You can define the value as required.
tag	string	Yes	Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.
format	string	Yes	Format string used to output logs in a specified format. It can contain several elements, where the parameter type and privacy identifier are mandatory. Parameters labeled {public} are public data and are displayed in plaintext; parameters labeled {private} (default value) are private data and are filtered by <private>.
args	any[]	Yes	Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.

Example

This example is used to output a WARN log with the format string being "%{public}s World %{private}d". The variable %{public}s is a plaintext string, and the variable %{private}d is a private integer.

hilog.warn(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3);

If "hello" is filled in %{public}s and 3 in %{private}d, the output log is as follows:

08-05 12:21:47.579  2695-2703/com.example.myapplication W 00001/testTag: hello World <private>

hilog.error

error(domain: number, tag: string, format: string, …args: any[]) : void

Prints ERROR logs.

System capability: SystemCapability.HiviewDFX.HiLog

Parameters

Name	Type	Mandatory	Description
domain	number	Yes	Service domain of logs. The value ranges from 0x0 to 0xFFFF. You can define the value as required.
tag	string	Yes	Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.
format	string	Yes	Format string used to output logs in a specified format. It can contain several elements, where the parameter type and privacy identifier are mandatory. Parameters labeled {public} are public data and are displayed in plaintext; parameters labeled {private} (default value) are private data and are filtered by <private>.
args	any[]	Yes	Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.

Example

This example is used to output an ERROR log with the format string being "%{public}s World %{private}d". The variable %{public}s is a plaintext string, and the variable %{private}d is a private integer.

hilog.error(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3);

If "hello" is filled in %{public}s and 3 in %{private}d, the output log is as follows:

08-05 12:21:47.579  2695-2703/com.example.myapplication E 00001/testTag: hello World <private>

hilog.fatal

fatal(domain: number, tag: string, format: string, …args: any[]) : void

Prints FATAL logs.

System capability: SystemCapability.HiviewDFX.HiLog

Parameters

Name	Type	Mandatory	Description
domain	number	Yes	Service domain of logs. The value ranges from 0x0 to 0xFFFF. You can define the value as required.
tag	string	Yes	Log tag in the string format. You are advised to use this parameter to identify a particular service behavior or the class holding the ongoing method.
format	string	Yes	Format string used to output logs in a specified format. It can contain several elements, where the parameter type and privacy identifier are mandatory. Parameters labeled {public} are public data and are displayed in plaintext; parameters labeled {private} (default value) are private data and are filtered by <private>.
args	any[]	Yes	Variable-length parameter list corresponding to the format string. The number and type of parameters must map to the identifier in the format string.

Example

This example is used to output a FATAL log with the format string being "%{public}s World %{private}d". The variable %{public}s is a plaintext string, and the variable %{private}d is a private integer.

hilog.fatal(0x0001, "testTag", "%{public}s World %{private}d", "hello", 3);

If "hello" is filled in %{public}s and 3 in %{private}d, the output log is as follows:

08-05 12:21:47.579  2695-2703/com.example.myapplication F 00001/testTag: hello World <private>

Parameter Format

Parameters in the log are printed in the following format:

%{[private flag]}specifier

Privacy Flag	Description
Unspecified	The default value is private, indicating that parameters in plaintext are not printed.
private	Prints private parameters.
public	Prints parameters in plaintext.

Specifier	Description	Example
d/i	Prints logs of the number and bigint types.	123
s	Prints logs of the string undefined bool and null types.	“123”

Example

let testObj: Record<string, string|number> = {
    'name': "Jack",
    'age': 22
}
let isBol = true;
let bigNum = BigInt(1234567890123456789);
hilog.info(0x0001, "jsHilogTest", "print object: %{public}s", JSON.stringify(testObj));
hilog.info(0x0001, "jsHilogTest", "private flag: %{private}s %s, print null: %{public}s", "hello", "world", null);
hilog.info(0x0001, "jsHilogTest", "print undefined: %{public}s", undefined);
hilog.info(0x0001, "jsHilogTest", "print number: %{public}d %{public}i", 123, 456);
hilog.info(0x0001, "jsHilogTest", "print bigNum: %{public}d %{public}i", bigNum, bigNum);
hilog.info(0x0001, "jsHilogTest", "print boolean: %{public}s", isBol);

Log printing result:

08-09 13:26:29.094  2266  2266 I A00001/jsHilogTest: print object: {"name":"Jack","age":22}
08-09 13:26:29.094  2266  2266 I A00001/jsHilogTest: private flag: <private> <private>, print null: null
08-09 13:26:29.094  2266  2266 I A00001/jsHilogTest: print undefined: undefined
08-09 13:26:29.094  2266  2266 I A00001/jsHilogTest: print number: 123 456
08-09 13:26:29.095  2266  2266 I A00001/jsHilogTest: print bigNum: 1234567890123456768 1234567890123456768
08-09 13:26:29.095  2266  2266 I A00001/jsHilogTest: print boolean: true