example_test.go

// Copyright (c) 2016 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package zap_test

import (
	"time"

	"github.com/uber-common/zap"
)

func Example() {
	// Log in JSON, using zap's reflection-free JSON encoder.
	// The default options will log any Info or higher logs to standard out.
	logger := zap.NewJSON()
	// For repeatable tests, pretend that it's always 1970.
	logger.StubTime()

	logger.Warn("Log without structured data...")
	logger.Warn(
		"Or use strongly-typed wrappers to add structured context.",
		zap.String("library", "zap"),
		zap.Duration("latency", time.Nanosecond),
	)

	// Avoid re-serializing the same data repeatedly by creating a child logger
	// with some attached context. That context is added to all the child's
	// log output, but doesn't affect the parent.
	child := logger.With(zap.String("user", "jane@test.com"), zap.Int("visits", 42))
	child.Error("Oh no!")

	// Output:
	// {"msg":"Log without structured data...","level":"warn","ts":0,"fields":{}}
	// {"msg":"Or use strongly-typed wrappers to add structured context.","level":"warn","ts":0,"fields":{"library":"zap","latency":1}}
	// {"msg":"Oh no!","level":"error","ts":0,"fields":{"user":"jane@test.com","visits":42}}
}

func ExampleNest() {
	logger := zap.NewJSON()
	// Stub the current time in tests.
	logger.StubTime()

	// We'd like the logging context to be {"outer":{"inner":42}}
	nest := zap.Nest("outer", zap.Int("inner", 42))
	logger.Info("Logging a nested field.", nest)

	// Output:
	// {"msg":"Logging a nested field.","level":"info","ts":0,"fields":{"outer":{"inner":42}}}
}

func ExampleNewJSON() {
	// The default logger outputs to standard out and only writes logs that are
	// Info level or higher.
	logger := zap.NewJSON()
	// Stub the current time in tests.
	logger.StubTime()

	// The default logger does not print Debug logs.
	logger.Debug("this won't be printed")
	logger.Info("This is an info log.")

	// Output:
	// {"msg":"This is an info log.","level":"info","ts":0,"fields":{}}
}

func ExampleNewJSON_options() {
	// We can pass multiple options to the NewJSON method to configure
	// the logging level, output location, or even the initial context.
	logger := zap.NewJSON(
		zap.Debug,
		zap.Fields(zap.Int("count", 1)),
	)
	// Stub the current time in tests.
	logger.StubTime()

	logger.Debug("This is a debug log.")
	logger.Info("This is an info log.")

	// Output:
	// {"msg":"This is a debug log.","level":"debug","ts":0,"fields":{"count":1}}
	// {"msg":"This is an info log.","level":"info","ts":0,"fields":{"count":1}}
}