diff --git a/cmd/gmqttd/command/start.go b/cmd/gmqttd/command/start.go
index 4a77bfbd..9da6a6b7 100644
--- a/cmd/gmqttd/command/start.go
+++ b/cmd/gmqttd/command/start.go
@@ -127,18 +127,11 @@ func NewStartCmd() *cobra.Command {
 			if useDefault {
 				l.Warn("config file not exist, use default configration")
 			}
-			hook := server.Hooks{
-				OnBasicAuth: func(ctx context.Context, client server.Client, req *server.ConnectRequest) (err error) {
-					fmt.Println(req.Options.SessionExpiry)
-					return nil
-				},
-			}
 			s := server.New(
 				server.WithConfig(c),
 				server.WithTCPListener(tcpListeners...),
 				server.WithWebsocketServer(websockets...),
 				server.WithLogger(l),
-				server.WithHook(hook),
 			)
 			err = s.Init()
 			if err != nil {
diff --git a/cmd/gmqttd/default_config.yml b/cmd/gmqttd/default_config.yml
index 3ad5aefe..b5f1f662 100644
--- a/cmd/gmqttd/default_config.yml
+++ b/cmd/gmqttd/default_config.yml
@@ -64,6 +64,7 @@ plugins:
       addr: 8084
 log:
   level: info # debug | info | warn | error
+  format: text # json | text
 
 
 
diff --git a/config/config.go b/config/config.go
index d071b158..eba726c0 100644
--- a/config/config.go
+++ b/config/config.go
@@ -1,7 +1,9 @@
 package config
 
 import (
+	"fmt"
 	"io/ioutil"
+	"os"
 
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
@@ -22,23 +24,27 @@ type Configuration interface {
 	yaml.Unmarshaler
 }
 
-// RegisterDefaultPluginConfig registers the default configuration for the given plugin name.
+// RegisterDefaultPluginConfig registers the default configuration for the given plugin.
 func RegisterDefaultPluginConfig(name string, config Configuration) {
+	if _, ok := defaultPluginConfig[name]; ok {
+		panic(fmt.Sprintf("duplicated default config for %s plugin", name))
+	}
 	defaultPluginConfig[name] = config
+
 }
 
 // DefaultConfig return the default configuration.
 // If config file is not provided, gmqttd will start with DefaultConfig.
-// Command-line flags will override the configuration.
 func DefaultConfig() Config {
 	c := Config{
 		Listeners: DefaultListeners,
 		MQTT:      DefaultMQTTConfig,
 		Log: LogConfig{
-			Level: "info",
+			Level:  "info",
+			Format: "text",
 		},
 		PidFile:           getDefaultPidFile(),
-		Plugins:           make(PluginConfig),
+		Plugins:           make(pluginConfig),
 		Persistence:       DefaultPersistenceConfig,
 		TopicAliasManager: DefaultTopicAliasManager,
 	}
@@ -65,12 +71,27 @@ var DefaultListeners = []*ListenerConfig{
 
 // LogConfig is use to configure the log behaviors.
 type LogConfig struct {
+	// Level is the log level. Possible values: debug, info, warn, error
 	Level string
+	// Format is the log format. Possible values: json, text
+	Format string
+}
+
+func (l LogConfig) Validate() error {
+	if l.Level != "debug" && l.Level != "info" && l.Level != "warn" && l.Level != "error" {
+		return fmt.Errorf("invalid log level: %s", l.Level)
+	}
+	if l.Format != "json" && l.Format != "text" {
+		return fmt.Errorf("invalid log format: %s", l.Format)
+	}
+	return nil
 }
 
-type PluginConfig map[string]Configuration
+// pluginConfig stores the plugin default configuration, key by the plugin name.
+// If the plugin has default configuration, it should call RegisterDefaultPluginConfig in it's init function to register.
+type pluginConfig map[string]Configuration
 
-func (p PluginConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
+func (p pluginConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	for _, v := range p {
 		err := unmarshal(v)
 		if err != nil {
@@ -86,7 +107,7 @@ type Config struct {
 	MQTT              MQTT              `yaml:"mqtt,omitempty"`
 	Log               LogConfig         `yaml:"log"`
 	PidFile           string            `yaml:"pid_file"`
-	Plugins           PluginConfig      `yaml:"plugins"`
+	Plugins           pluginConfig      `yaml:"plugins"`
 	Persistence       Persistence       `yaml:"persistence"`
 	TopicAliasManager TopicAliasManager `yaml:"topic_alias_manager"`
 }
@@ -116,7 +137,7 @@ func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		raw.MQTT = DefaultMQTTConfig
 	}
 	if len(raw.Plugins) == 0 {
-		raw.Plugins = make(PluginConfig)
+		raw.Plugins = make(pluginConfig)
 		for name, v := range defaultPluginConfig {
 			raw.Plugins[name] = v
 		}
@@ -140,6 +161,7 @@ func (c Config) Validate() error {
 	if err != nil {
 		return err
 	}
+
 	for _, conf := range c.Plugins {
 		err := conf.Validate()
 		if err != nil {
@@ -175,9 +197,14 @@ func (c Config) GetLogger(config LogConfig) (l *zap.Logger, err error) {
 	if err != nil {
 		return
 	}
+	var core zapcore.Core
+	if config.Format == "json" {
+		core = zapcore.NewCore(zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()), os.Stdout, logLevel)
+	}
+	if config.Format == "text" {
+		core = zapcore.NewCore(zapcore.NewConsoleEncoder(zap.NewDevelopmentEncoderConfig()), os.Stdout, logLevel)
+	}
 
-	lc := zap.NewDevelopmentConfig()
-	lc.Level = zap.NewAtomicLevelAt(logLevel)
-	l, err = lc.Build()
-	return l, nil
+	zaplog := zap.New(core, zap.AddStacktrace(zap.ErrorLevel), zap.AddCaller())
+	return zaplog, nil
 }
diff --git a/server/client.go b/server/client.go
index 1047f1c2..e79ddea0 100644
--- a/server/client.go
+++ b/server/client.go
@@ -589,7 +589,6 @@ func (client *client) connectWithTimeOut() (ok bool) {
 					Code:       codeErr.Code,
 					Properties: getErrorProperties(client, &codeErr.ErrorDetails),
 				}
-				fmt.Println(getErrorProperties(client, &codeErr.ErrorDetails))
 				return
 			}
 			// authentication success