我要评论背景
spring 提供了 @restcontrolleradvice 用来实现 http 协议的全局异常处理。在异常信息的处理上通常只返回特定的 response 对象，如下。
@slf4j
@restcontrolleradvice
public class restexceptionresolver {
@exceptionhandler(exception.class)
public responseentity<?> processexception(exception ex) {
bodybuilder builder;
response response;
responsestatus responsestatus =
annotationutils.findannotation(ex.getclass(), responsestatus.class);
if (responsestatus != null) {
builder = responseentity.status(responsestatus.value());
response = response.buildfailure("500", responsestatus.reason());
} else {
builder = responseentity.status(httpstatus.internal_server_error);
response = response.buildfailure("500", ex.getmessage());
}
this.process(ex, response);
return builder.body(response);
}
}
作为基础框架，笔者就遇到项目a 要求返回 response1 对象，项目b 要求返回 response2 对象，这个时候，适配起来就很痛苦，例如下方的代码。
@slf4j
@noargsconstructor
@allargsconstructor
@equalsandhashcode(callsuper = false)
@tostring(callsuper = true)
@data
public class response extends dto {
private static final long serialversionuid = 1l;
private boolean success;
private string errcode; // 项目a 要求错误码是字符型
private string errmessage; // 项目a 要求用这个名字
private int code; // 项目b 要求错误码是整型
private string message; // 项目b 要求用这个名字
}
另外，@restcontrolleradvice 只适用于 web 异常捕获，我们还要考虑其他组件的情况，例如 dubbo 捕获 rpc 异常、sentinel 组件触发限流、spring security 安全框架抛出认证异常。
目标
不需要修改基础框架，允许业务方自行扩展异常返回对象。
实现
将 response 提炼为 builder 模式，改为 responsebuilder.builder() 构建返回对象。
@slf4j
@restcontrolleradvice
public class restexceptionhandler {
@exceptionhandler(exception.class)
public responseentity<?> resolveexception(exception ex) {
bodybuilder builder;
object response;
responsestatus status = annotationutils.findannotation(ex.getclass(), responsestatus.class);
if (status != null) {
builder = responseentity.status(status.value());
response = responsebuilder.builder().buildfailure("500", status.reason());
} else {
builder = responseentity.status(httpstatus.internal_server_error);
response = responsebuilder.builder().buildfailure("500", ex.getmessage());
}
this.postprocess(ex);
return builder.body(response);
}
}
public interface responsebuilder<t> {
static responsebuilder<?> builder() {
// 尝试从业务项目获取自定义的 spring bean
responsebuilder<?> builder = applicationcontexthelper.getbean(responsebuilder.class);
if (builder != null) {
return builder;
}
// 如果业务项目没有自定义 bean，返回默认的 builder
return defalutresponsebuilder.getinstance();
}
t buildsuccess();
<body> t buildsuccess(body data);
t buildfailure(string errcode, string errmessage, object... params);
}
public class defalutresponsebuilder implements responsebuilder<response> {
private static final defaultresponsebuilder instance = new defaultresponsebuilder();
private defaultresponsebuilder() {}
public static defaultresponsebuilder getinstance() {
return instance;
}
@override
public response buildsuccess() {
response response = new response();
response.setsuccess(true);
return response;
}
@override
public <body> response buildsuccess(body data) {
singleresponse<body> response = new singleresponse<>();
response.setsuccess(true);
response.setdata(data);
return response;
}
@override
public response buildfailure(string errcode, string errmessage, object... params) {
response response = new response();
response.setsuccess(false);
response.seterrcode(errcode);
response.seterrmessage(messageformatter.arrayformat(message, placeholders).getmessage());
return response;
}
}
@slf4j
@noargsconstructor
@allargsconstructor
@equalsandhashcode(callsuper = false)
@tostring(callsuper = true)
@data
public class response extends dto {
private static final long serialversionuid = 1l;
private boolean success;
private string errcode;
private string errmessage;
}
业务方觉得 response 不能满足需求，重新定义了新对象，如下。
@slf4j
@noargsconstructor
@allargsconstructor
@equalsandhashcode(callsuper = false)
@tostring(callsuper = true)
@data
public class customresponse {
private static final long serialversionuid = 1l;
private boolean success;
private int code; // 要求错误码是整型
private string message; // 前端要求用这个名字
}创建 customresponsebuilder 包装 customresponse 对象，并标记 @component 注解，放入 spring bean 管理。
@component
public class customresponsebuilder implements responsebuilder<customresponse> {
@override
public customresponse buildsuccess() {
customresponse response = new customresponse();
response.setsuccess(true);
return response;
}
@override
public <body> customresponse buildsuccess(body data) {
// 略
}
@override
public customresponse buildfailure(int code, string message, object... params) {
customresponse response = new customresponse();
response.setsuccess(false);
response.setcode(code);
response.setmessage(messageformatter.arrayformat(message, placeholders).getmessage());
return response;
}
}
上述已提到 responsebuilder.builder() 优先查找 spring bean，所以 customresponsebuilder 覆盖了框架内置的 defaultresponsebuilder 类，全局异常捕获器返回结果时，就能返回业务方自定义的 customresponse 对象，这样，不需要改动框架，就能满足业务需求。
产出
根据这个思路，我们分别实现了 web 异常、dubbo 异常、sentinel 限流、security 认证等各种场景的异常处理机制，业务方只需要自行创建 responsebuilder 扩展自己的返回对象即可，不需要修改框架。
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