我最近将MYSQL数据库从5.7版更新到了8版，因此将MYSQL连接器依赖关系从5版更新到8版，并使用最新版本的c3p0 0.9.5版更新到Clojure项目。更新后，我在请求数据库时遇到c3p0连接池错误。
以下是例外情况的一部分：
com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection (C3P0PooledConnectionPool.java:692)
com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection (AbstractPoolBackedDataSource.java:140)
clojure.java.jdbc$get_connection.invoke (jdbc.clj:278)
clojure.java.jdbc$db_query_with_resultset.invoke (jdbc.clj:798)
clojure.java.jdbc$query.doInvoke (jdbc.clj:832)
clojure.lang.RestFn.invoke (RestFn.java:425)
以下是可能影响c3p0连接池的依赖项：
[postgresql "9.1-901-1.jdbc4"]
[com.mchange/c3p0 "0.9.5"]
[yesql "0.4.2"]
这是我连接c3p0的地方：
(ns myapp.database.database-pooling
(:import com.mchange.v2.c3p0.ComboPooledDataSource))
(defn pooled-database
[specification]
(let [cpds (doto (ComboPooledDataSource.)
(.setDriverClass (:classname specification))
(.setJdbcUrl (str "jdbc:" (:subprotocol specification) ":" (:subname specification)))
(.setUser (:user specification))
(.setPassword (:password specification))
;; expire excess connections after 30 minutes of inactivity:
(.setMaxIdleTimeExcessConnections (* 30 60))
;; expire connections after 3 hours of inactivity:
(.setMaxIdleTime (* 3 60 60)))]
{:datasource cpds}))
不幸的是，我还无法找到在线解决方案。
我不确定我在c3p0连接上做错了什么，因为我寻找了很多可能性，但仍然失败了。
我们将更加感激你的帮助。
我有一个使用H2数据库的旧演示，可能会有所帮助。源代码在这里。
project.clj
(defproject demo "0.1.0-SNAPSHOT"
:description "FIXME: write description"
:url "http://example.com/FIXME"
:license {:name "Eclipse Public License"
:url "http://www.eclipse.org/legal/epl-v10.html"}
:dependencies [
[com.h2database/h2 "1.4.197"]
[hikari-cp "2.3.0"]
[org.clojure/java.jdbc "0.7.5"]
[org.clojure/clojure "1.9.0"]
[org.clojure/spec.alpha "0.1.143"]
[org.clojure/test.check "0.9.0"]
[prismatic/schema "1.1.9"]
[tupelo "0.9.111"]
]
:profiles {:dev {:dependencies []
:plugins [[com.jakemccrary/lein-test-refresh "0.22.0"]
[lein-ancient "0.6.15"]
[lein-codox "0.10.3"]]}
:uberjar {:aot :all}}
:global-vars {*warn-on-reflection* false}
:main ^:skip-aot demo.core
:source-paths ["src"]
:test-paths ["src"]
:java-source-paths ["src-java"]
:target-path "target/%s"
:jvm-opts ["-Xms500m" "-Xmx2g"]
)
连接池部分看起来像：
(ns tst.demo.jdbc-pool
(:use demo.core
tupelo.core
tupelo.test)
(:require
[clojure.java.jdbc :as jdbc]
[hikari-cp.core :as pool]
))
(def datasource-options-sample {:auto-commit true
:read-only false
:connection-timeout 30000
:validation-timeout 5000
:idle-timeout 600000
:max-lifetime 1800000
:minimum-idle 10
:maximum-pool-size 10
:pool-name "db-pool"
:adapter "h2" ; "postgresql"
:username "sa"
:password ""
:database-name "database"
:server-name "localhost"
:port-number 5432
:register-mbeans false})
(def datasource-options {:adapter "h2"
:url "jdbc:h2:mem:demo;DB_CLOSE_DELAY=-1"
:username "sa"
:password ""})
(def ^:dynamic db-conn nil)
(defn with-connection-pool
"Creates and uses a connection for test function"
[tst-fn]
(let [datasource (pool/make-datasource datasource-options)]
(binding [db-conn {:datasource datasource}]
(tst-fn)
(pool/close-datasource datasource)))) ; close the connection - also closes/destroys the in-memory database
(use-fixtures
:once with-connection-pool) ; use the same db connection pool for all tests
(dotest
; creates & drops a connection (& transaction) for each command
(jdbc/db-do-commands db-conn ["drop table if exists langs"
"drop table if exists releases"])
(jdbc/db-do-commands
db-conn
[(jdbc/create-table-ddl :langs
[[:id :serial]
[:lang "varchar not null"]])
(jdbc/create-table-ddl :releases
[[:id :serial]
[:desc "varchar not null"]
[:langId "numeric"]])])
(jdbc/insert-multi! db-conn :langs ; => ({:id 1} {:id 2})
[{:lang "Clojure"}
{:lang "Java"}])
(let [result (jdbc/query db-conn ["select * from langs"])]
(is= result [{:id 1, :lang "Clojure"}
{:id 2, :lang "Java"}]))
; Wraps all commands in a single transaction
(jdbc/with-db-transaction
[tx db-conn]
(let [clj-id (grab :id (only (jdbc/query tx ["select id from langs where lang='Clojure'"])))]
(jdbc/insert-multi! tx :releases
[{:desc "ancients" :langId clj-id}
{:desc "1.8" :langId clj-id}
{:desc "1.9" :langId clj-id}]))
(let [java-id (grab :id (only (jdbc/query tx ["select id from langs where lang='Java'"])))]
(jdbc/insert-multi! tx :releases
[{:desc "dusty" :langId java-id}
{:desc "8" :langId java-id}
{:desc "9" :langId java-id}
{:desc "10" :langId java-id}])))
(let [
; note cannot wrap select list in parens or get "bulk" output
result-0 (jdbc/query db-conn ["select langs.lang, releases.desc
from langs join releases
on (langs.id = releases.langId)
where (lang = 'Clojure') "])
result-1 (jdbc/query db-conn ["select l.lang, r.desc
from langs as l
join releases as r
on (l.id = r.langId)
where (l.lang = 'Clojure') "])
result-2 (jdbc/query db-conn ["select langs.lang, releases.desc
from langs, releases
where ( (langs.id = releases.langId)
and (lang = 'Clojure') ) "])
result-3 (jdbc/query db-conn ["select l.lang, r.desc
from langs as l, releases as r
where ( (l.id = r.langId)
and (l.lang = 'Clojure') ) "])]
(let [expected [{:lang "Clojure", :desc "1.8"}
{:lang "Clojure", :desc "1.9"}
{:lang "Clojure", :desc "ancients"}]]
(set= expected result-0)
(set= expected result-1)
(set= expected result-2)
(set= expected result-3))
(println "all tests finished") ) )
要运行，只需键入：
> lein clean ; lein test
----------------------------------
Clojure 1.9.0 Java 15.0.2
----------------------------------
lein test tst.demo.jdbc
result-0 =>
({:lang "Clojure", :desc "ancients"}
{:lang "Clojure", :desc "1.8"}
{:lang "Clojure", :desc "1.9"})
lein test tst.demo.jdbc-pool
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
all tests finished
Ran 3 tests containing 7 assertions.
0 failures, 0 errors.