docs(logger): formatter (#3835)

docs/source/en/core/logger.md

@@ -233,6 +233,30 @@ module.exports = appInfo => {
 
 Now, you can get loggers via `app.getLogger('xxLogger')` or `ctx.getLogger('xxLogger')`, and the logs printed from those loggers are similar to the ones from `coreLogger`.
 
+### Custom logger formatter
+
+```js
+// config/config.${env}.js
+const path = require('path');
+
+module.exports = appInfo => {
+  return {
+    customLogger: {
+      xxLogger: {
+        file: path.join(appInfo.root, 'logs/xx.log'),
+        formatter(meta) {
+          return `[${meta.date}] ${meta.message}`;
+        },
+        // ctx logger
+        contextFormatter(meta) {
+          return `[${meta.date}] [${meta.ctx.method} ${meta.ctx.url}] ${meta.message}`;
+        },
+      },
+    },
+  };
+};
+```
+
 ### Advanced
 
 Logs will be written into files by default. Further, they will also be printed into terminal in development. But what if we need to print those into another place? Creating customized transport can take you there.

docs/source/zh-cn/core/logger.md

@@ -244,6 +244,30 @@ module.exports = appInfo => {
 
 可通过 `app.getLogger('xxLogger')` / `ctx.getLogger('xxLogger')` 获取，最终的打印结果和 coreLogger 类似。
 
+### 自定义日志格式
+
+```js
+// config/config.${env}.js
+const path = require('path');
+
+module.exports = appInfo => {
+  return {
+    customLogger: {
+      xxLogger: {
+        file: path.join(appInfo.root, 'logs/xx.log'),
+        formatter(meta) {
+          return `[${meta.date}] ${meta.message}`;
+        },
+        // ctx logger
+        contextFormatter(meta) {
+          return `[${meta.date}] [${meta.ctx.method} ${meta.ctx.url}] ${meta.message}`;
+        },
+      },
+    },
+  };
+};
+```
+
 ### 高级自定义日志
 
 日志默认是打印到日志文件中，当本地开发时同时会打印到终端。