Overview

This tool is a command line app which parses json logs produced by a Java application and outputs them formatted as a plain text.

This tool is useful when investigating logs without requiring 3rd party tooling like (Google Cloud logs or Kibana). This is especially useful when trying to read/investigate exceptions as it formats the stacktraces over multiple lines.

Installing

make install

This will install json-log-parser into the ~/go/bin/ directory.

Command line args

Usage of json-log-parser:
  -file string
        json log file to read from - if not supplied then stdin is used
  -out string
        output file to write the parsed logs to - if not supplied then stdout is used
  -severity string
        min severity level to filter on, one of: [trace debug info warn error] (default "info")

Example commands

These commands assume that json-log-parser has been installed and is available on the PATH.

Format k8s logs

One scenario that this works particular well for, retrieving logs from a k8s pod using kubectl. Example command:

kubectl logs POD-NAME | json-log-parser

JSON log file structure

Example log object:

 {
    "timestamp":"2024-06-10T08:46:25.518Z",
    "level":"ERROR",
    "thread":"thread-12",
    "logger":"com.blah.SomeClass",
    "message":"Something went wrong, see exception for details",
    "exception":"java.lang.NullPointerException: null\n\tat java.base/java.util.Objects.requireNonNull(Unknown Source)\n\tredacted..."
 }

A log file contains a log object per line and not an array of logs objects.

Output format

Example formatted plain text log line output by the tool:

2024-06-10T08:46:25.518Z [thread-12] ERROR com.blah.SomeClass Something went wrong, see exception for details java.lang.NullPointerException: null
        at java.base/java.util.Objects.requireNonNull(Unknown Source)
        redacted...

Future work

• support for logging java mdc (mapped diagnostic context)
• support other languages / json log formats
• allow output format to be customised
• further log filtering