中间件与路由处理器

Posted 2020-09-29 火磷

路由处理器和中间件的参数中都有回调函数，这个函数有2个3个或4个参数。
如果有2个或3个参数，前两个参数是请求和响应对象，第三个参数是next函数。
如果有4个参数，它就变成了错误处理中间件，第一个参数变成了错误对象，然后依次是请求、响应和next对象。
如果不调用next()，管道就会被终止，也不会再有处理器或中间件做后续处理，此时应该发送一个响应到客户端。

 1 var app = require(\'express\')();
 2 let i=1;
 3 app.use(function(req, res, next){
 4     console.log(\'\\nALLWAYS\'+i++);
 5     next();
 6 });
 7 app.use(function(req, res, next){
 8     console.log(\'SOMETIMES\');
 9     next();
10 });
11 //错误处理中间件
12 app.use(function(err, req, res, next){
13     console.log(\'unhandled error detected: \' + err.message);
14     res.send(\'500 - server error\');
15 });
16 app.use(function(req, res){
17     console.log(\'route not handled\');
18     res.send(\'404 - not found\');
19 });
20 app.listen(3000, function(){
21     console.log(\'listening on 3000\');
22 });

 

 1 var app = require(\'express\')();
 2 let i=1;
 3 app.use(function(req, res, next){
 4       console.log(\'\\nALLWAYS\'+i++);
 5       next();
 6 });
 7 app.get(\'/a\', function(req, res){
 8       console.log(\'/a: route terminated\');
 9       res.send(\'a\');
10 });
11 app.get(\'/a\', function(req, res){
12       console.log(\'/a: never called\');
13 });
14 app.use(function(req, res, next){
15       console.log(\'SOMETIMES\');
16       next();
17 });
18 //错误处理中间件
19 app.use(function(err, req, res, next){
20       console.log(\'unhandled error detected: \' + err.message);
21       res.send(\'500 - server error\');
22 });
23 app.use(function(req, res){
24       console.log(\'route not handled\');
25       res.send(\'404 - not found\');
26 });
27 app.listen(3000, function(){
28       console.log(\'listening on 3000\');
29 });

 

 1 var app = require(\'express\')();
 2 let i=1;
 3 app.use(function(req, res, next){
 4       console.log(\'\\nALLWAYS\'+i++);
 5       next();
 6 });
 7 app.get(\'/b\', function(req, res, next){
 8       console.log(\'/b: route not terminated\');
 9       next();
10 });
11 app.use(function(req, res, next){
12       console.log(\'SOMETIMES\');
13       next();
14 });
15 app.get(\'/b\', function(req, res, next){
16       console.log(\'/b (part 2): error thrown\' );
17       throw new Error(\'b failed\');
18 });
19 app.use(\'/b\', function(err, req, res, next){
20       console.log(\'/b error detected and passed on\');
21       next(err);
22 });
23 //错误处理中间件
24 app.use(function(err, req, res, next){
25       console.log(\'unhandled error detected: \' + err.message);
26       res.send(\'500 - server error\');
27 });
28 app.use(function(req, res){
29       console.log(\'route not handled\');
30       res.send(\'404 - not found\');
31 });
32 app.listen(3000, function(){
33       console.log(\'listening on 3000\');
34 });

 

 

 1 var app = require(\'express\')();
 2 let i=1;
 3 app.use(function(req, res, next){
 4     console.log(\'\\nALLWAYS\'+i++);
 5     next();
 6 });
 7 app.use(function(req, res, next){
 8     console.log(\'SOMETIMES\');
 9     next();
10 });
11 app.get(\'/c\', function(err, req){
12     console.log(\'/c: error thrown\');
13     throw new Error(\'c failed\');
14 });
15 app.use(\'/c\', function(err, req, res, next){
16     console.log(\'/c: error deteccted but not passed on\');
17     next();
18 });
19 //错误处理中间件
20 app.use(function(err, req, res, next){
21     console.log(\'unhandled error detected: \' + err.message);
22     res.send(\'500 - server error\');
23 });
24 app.use(function(req, res){
25     console.log(\'route not handled\');
26     res.send(\'404 - not found\');
27 });
28 app.listen(3000, function(){
29     console.log(\'listening on 3000\');
30 });