JAVA基礎26-資料庫連線池
資料庫連線池
資料庫連線池負責分配，管理，釋放資料庫連線，它允許應用程式重複使用一個現有的資料庫連線，而不是重新建立一個。
編寫資料庫連線池
- 編寫資料庫連線池必須實現java.sql.DataSource介面
- 在DataSource建構函式中批量建立與資料庫的連線，並把建立的連線加入LinkedList物件中。
- 實現getConnection方法，讓getConnection方法每次呼叫時，從LinkedList中取一個Connection返回給使用者。
- 當用戶使用完Connection，呼叫Connection.close()方法時，Collection物件應保證將自己返回到LinkedList中,而不要把conn還給資料庫。Collection保證將自己返回到LinkedList中是此處程式設計的難點。
package com.demo.demo.demo1; import java.io.PrintWriter; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.sql.SQLFeatureNotSupportedException; import java.util.LinkedList; import java.util.logging.Logger; import javax.sql.ConnectionPoolDataSource; import javax.sql.DataSource; public class ConnetionPool implements DataSource { private static LinkedList<Connection> connPool=new LinkedList<>(); static{ String dirver = "com.mysql.jdbc.Driver"; String url = "JDBC:mysql://localhost:3306/world"; String user = "root"; String passwd = "1234"; try { Class.forName(dirver); for(int i=0;i<50;i++){ { Connection c=DriverManager.getConnection(url,user,passwd); connPool.add(c); } } } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } @Override public PrintWriter getLogWriter() throws SQLException { // TODO Auto-generated method stub return null; } @Override public void setLogWriter(PrintWriter out) throws SQLException { // TODO Auto-generated method stub } @Override public void setLoginTimeout(int seconds) throws SQLException { // TODO Auto-generated method stub } @Override public int getLoginTimeout() throws SQLException { // TODO Auto-generated method stub return 0; } @Override public Logger getParentLogger() throws SQLFeatureNotSupportedException { // TODO Auto-generated method stub return null; } @Override public <T> T unwrap(Class<T> iface) throws SQLException { // TODO Auto-generated method stub return null; } @Override public boolean isWrapperFor(Class<?> iface) throws SQLException { // TODO Auto-generated method stub return false; } @Override public Connection getConnection() throws SQLException { if(connPool.size()>0){ final Connection c=connPool.removeFirst(); return (Connection) Proxy.newProxyInstance(ConnetionPool.class.getClassLoader(), c.getClass().getInterfaces(), new InvocationHandler(){ @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { if(!method.getName().equals("close")){ //呼叫的不是close方法 return method.invoke(c,args); } else{ //呼叫的是close方法 connPool.add(c); return null; } } }); }else{ throw new RuntimeException("資料庫繁忙"); } } private InvocationHandler InvocationHandler() { // TODO Auto-generated method stub return null; } @Override public Connection getConnection(String username, String password) throws SQLException { // TODO Auto-generated method stub return null; } }
三：開源的資料庫連線池
3-1：DBCP，Druid，C3P0資料庫連線池
|
|
DBCP |
c3p0 |
Druid |
|---|---|---|---|
| 使用者名稱 |
username |
user |
username |
| 密碼 |
password |
password |
password |
| URL |
url |
jdbcUrl |
jdbcUrl |
| 驅動類名 |
driverClassName |
driverClass |
driverClassName （若不指定，可通過jdbcUrl自動識別） |
| 最小連線數 |
minIdle(0) |
minPoolSize(3) |
minIdle(0) |
| 初始化連線數 |
initialSize(0) |
initialPoolSize(3) |
initialSize(0) |
| 最大連線數 |
maxTotal(8) |
maxPoolSize(15) |
maxActive(8) |
| 最大等待時間 |
maxWaitMillis(毫秒) |
maxIdleTime(0秒) |
maxWait(毫秒) |
| 開啟快取功能 |
poolPreparedStatements |
maxStatements |
poolPreparedStatements |
| 單個連線擁有的最大快取數 |
maxOpenPrepared- Statements |
maxStatementsPer- Connection |
maxOpenPrepared- Statements |
| 申請連線檢測 |
testOnBorrow |
testConnectionOnCheckin |
testOnBorrow |
| 是否超時檢測 |
testWhileIdle |
|
testWhileIdle |
| 空閒時間 |
timeBetweenEvictionRunsMillis |
idleConnectionTestPeriod |
timeBetweenEvictionRunsMillis |
| 校驗用sql語句 |
validationQuery |
preferredTestQuery |
validationQuery |
| 歸還連線檢測 |
testOnReturn |
testConnectionOnCheckout |
testOnReturn |
| 重連次數 |
|
acquireRetryAttempts |
|
| 間隔時間 |
|
acquireRetryDelay |
|
3-2配置詳情
3-2-1 DBCP 屬性說明表
| 屬性(Parameter) |
預設值(Default) |
描述(Description) |
| username |
|
傳遞給JDBC驅動的用於建立連線的使用者名稱(The connection username to be passed to our JDBC driver to establish a connection.) |
| password |
|
傳遞給JDBC驅動的用於建立連線的密碼(The connection password to be passed to our JDBC driver to establish a connection.) |
| url |
|
傳遞給JDBC驅動的用於建立連線的URL(The connection URL to be passed to our JDBC driver to establish a connection.) |
| driverClassName |
|
使用的JDBC驅動的完整有效的java 類名(The fully qualified Java class name of the JDBC driver to be used.) |
| defaultAutoCommit |
driver default |
連線池建立的連線的預設的auto-commit狀態,沒有設定則不會自動提交(The default auto-commit state of connections created by this pool. If not set then the setAutoCommit method will not be called.) |
| initialSize |
0 |
初始化連線:連線池啟動時建立的初始化連線數量(The initial number of connections that are created when the pool is started. |
| maxTotal |
8 |
最大活動連線:連線池在同一時間能夠分配的最大活動連線的數量, 如果設定為非正數則表示不限制(The maximum number of active connections that can be allocated from this pool at the same time, or negative for no limit.) |
| maxIdle |
8 |
最大空閒連線:連線池中容許保持空閒狀態的最大連線數量,超過的空閒連線將被釋放,如果設定為負數表示不限制(The maximum number of connections that can remain idle in the pool, without extra ones being released, or negative for no limit.) |
| minIdle |
0 |
最小空閒連線:連線池中容許保持空閒狀態的最小連線數量,負數表示沒有現在(The maximum number of connections that can remain idle in the pool, without extra ones being released, or negative for no limit.) |
| 注意：如果在某些負載比較大的系統中將maxIdel設定過小時，很可能會出現連線關閉的同時新連線馬上開啟的情況.這是由於關閉連線的執行緒比開啟的快導致的.所以，對於這種系統中,maxIdle的設定值是不同的但是通常首選預設值 |
||
| (NOTE: If maxIdle is set too low on heavily loaded systems it is possible you will see connections being closed and almost immediately new connections being opened. This is a result of the active threads momentarily closing connections faster than they are opening them, causing the number of idle connections to rise above maxIdle. The best value for maxIdle for heavily loaded system will vary but the default is a good starting point.) |
||
| maxWaitMillis |
indefinitely |
最大等待時間:當沒有可用連線時,連線池等待連線被歸還的最大時間(以毫秒計數),超過時間則丟擲異常,如果設定為-1表示無限等待(The maximum number of milliseconds that the pool will wait (when there are no available connections) for a connection to be returned before throwing an exception, or -1 to wait indefinitely.) |
| validationQuery |
|
SQL查詢,用來驗證從連線池取出的連線,在將連線返回給呼叫者之前.如果指定,則查詢必須是一個SQL SELECT並且必須返回至少一行記錄(The SQL query that will be used to validate connections from this pool before returning them to the caller. If specified, this query MUST be an SQL SELECT statement that returns at least one row. If not specified, connections will be validation by calling the isValid() method.) |
| testOnCreate |
false |
指明是否在建立連線之後進行驗證,如果驗證失敗,則嘗試重新建立連線(The indication of whether objects will be validated after creation. If the object fails to validate, the borrow attempt that triggered the object creation will fail.) |
| testOnBorrow |
true |
指明是否在從池中取出連線前進行檢驗,如果檢驗失敗,則從池中去除連線並嘗試取出另一個. 注意: 設定為true後如果要生效,validationQuery引數必須設定為非空字串(The indication of whether objects will be validated before being borrowed from the pool. If the object fails to validate, it will be dropped from the pool, and we will attempt to borrow another.) |
| testOnReturn |
false |
指明是否在歸還到池中前進行檢驗(The indication of whether objects will be validated before being returned to the pool.) |
| testWhileIdle |
false |
指明連線是否被空閒連接回收器(如果有)進行檢驗.如果檢測失敗,則連線將被從池中去除. 注意: 設定為true後如果要生效,validationQuery引數必須設定為非空字串(The indication of whether objects will be validated by the idle object evictor (if any). If an object fails to validate, it will be dropped from the pool.) |
| timeBetweenEviction- RunsMillis |
-1 |
在空閒連接回收器執行緒執行期間休眠的時間值,以毫秒為單位.如果設定為非正數,則不執行空閒連接回收器執行緒(The number of milliseconds to sleep between runs of the idle object evictor thread. When non-positive, no idle object evictor thread will be run.) |
| numTestsPerEvictionRun |
3 |
在每次空閒連接回收器執行緒(如果有)執行時檢查的連線數量(The number of objects to examine during each run of the idle object evictor thread (if any).) |
| minEvictableIdleTime-Millis |
1000*60*30 |
連線在池中保持空閒而不被空閒連接回收器執行緒(如果有)回收的最小時間值，單位毫秒(The minimum amount of time an object may sit idle in the pool before it is eligable for eviction by the idle object evictor (if any).) |
| softMiniEvictableIdle- TimeMillis |
-1 |
說明(The minimum amount of time a connection may sit idle in the pool before it is eligible for eviction by the idle connection evictor, with the extra condition that at least "minIdle" connections remain in the pool. When miniEvictableIdleTimeMillis is set to a positive value, miniEvictableIdleTimeMillis is examined first by the idle connection evictor - i.e. when idle connections are visited by the evictor, idle time is first compared against miniEvictableIdleTimeMillis (without considering the number of idle connections in the pool) and then against softMinEvictableIdleTimeMillis, including the minIdle constraint.) |
| maxConnLifetimeMillis |
-1 |
說明(The maximum lifetime in milliseconds of a connection. After this time is exceeded the connection will fail the next activation, passivation or validation test. A value of zero or less means the connection has an infinite lifetime.) |
| logExpiredConnections |
true |
說明(Flag to log a message indicating that a connection is being closed by the pool due to maxConnLifetimeMillis exceeded. Set this property to false to suppress expired connection logging that is turned on by default. |
| connectionInitSqls |
null |
說明(A Collection of SQL statements that will be used to initialize physical connections when they are first created. These statements are executed only once - when the configured connection factory creates the connection.) |
| info |
true |
說明(True means that borrowObject returns the most recently used ("last in") connection in the pool (if there are idle connections available). False means that the pool behaves as a FIFO queue - connections are taken from the idle instance pool in the order that they are returned to the pool.) |
| poolPreparedState-ments |
false |
開啟池的prepared statement 池功能(Enable prepared statement pooling for this pool.) |
| maxOpenPreparedState-ments |
unlimited |
statement池能夠同時分配的開啟的statements的最大數量, 如果設定為0表示不限制(The maximum number of open statements that can be allocated from the statement pool at the same time, or negative for no limit.) |
| NOTE - Make sure your connection has some resources left for the other statements. Pooling PreparedStatements may keep their cursors open in the database, causing a connection to run out of cursors, especially if maxOpenPreparedStatements is left at the default (unlimited) and an application opens a large number of different PreparedStatements per connection. To avoid this problem, maxOpenPreparedStatements should be set to a value less than the maximum number of cursors that can be open on a Connection. |
||
| accessToUnderlyingConnectionAllowed |
false |
控制PoolGuard是否容許獲取底層連線(Controls if the PoolGuard allows access to the underlying connection.) 預設false不開啟, 這是一個有潛在危險的功能, 不適當的編碼會造成傷害.(關閉底層連線或者在守護連線已經關閉的情況下繼續使用它).請謹慎使用,並且僅當需要直接訪問驅動的特定功能時使用.注意: 不要關閉底層連線, 只能關閉前面的那個. Default is false, it is a potential dangerous operation and misbehaving programs can do harmful things. (closing the underlying or continue using it when the guarded connection is already closed) Be careful and only use when you need direct access to driver specific extensions. NOTE: Do not close the underlying connection, only the original one. |
| removeAbandoned |
false |
標記是否刪除洩露的連線,如果他們超過了removeAbandonedTimout的限制.如果設定為true, 連線被認為是被洩露並且可以被刪除,如果空閒時間超過removeAbandonedTimeout. 設定為true可以為寫法糟糕的沒有關閉連線的程式修復資料庫連線. (Flags to remove abandoned connections if they exceed the removeAbandonedTimout. A connection is considered abandoned and eligible for removal if it has not been used for longer than removeAbandonedTimeout. Setting one or both of these to true can recover db connections from poorly written applications which fail to close connections.) |
| removeAbandonedTimeout |
300 |
洩露的連線可以被刪除的超時值, 單位秒(Timeout in seconds before an abandoned connection can be removed.) |
| logAbandoned |
false |
標記當Statement或連線被洩露時是否列印程式的stack traces日誌。被洩露的Statements和連線的日誌新增在每個連線開啟或者生成新的Statement,因為需要生成stack trace。(Flag to log stack traces for application code which abandoned a Statement or Connection. Logging of abandoned Statements and Connections adds overhead for every Connection open or new Statement because a stack trace has to be generated.) |
| abandonedUsageTracking |
false |
如果為true, 那麼連線池會記錄每個方法呼叫時候的堆疊資訊以及廢棄連線的除錯資訊(If true, the connection pool records a stack trace every time a method is called on a pooled connection and retains the most recent stack trace to aid debugging of abandoned connections. There is significant overhead added by setting this to true.) |
| 注:如果開啟"removeAbandoned",那麼連線在被認為洩露時可能被池回收. 這個機制在(getNumIdle() < 2)and (getNumActive() > getMaxActive() - 3)時被觸發. 舉例當maxActive=20, 活動連線為18,空閒連線為1時可以觸發"removeAbandoned".但是活動連線只有在沒有被使用的時間超過"removeAbandonedTimeout"時才被刪除,預設300秒.在resultset中游歷不被計算為被使用. |
||
| If you have enabled removeAbandonedOnMaintenance or removeAbandonedOnBorrow then it is possible that a connection is reclaimed by the pool because it is considered to be abandoned. This mechanism is triggered when (getNumIdle() < 2) and (getNumActive() > getMaxTotal() - 3) and removeAbandonedOnBorrow is true; or after eviction finishes and removeAbandonedOnMaintenance is true. For example, maxTotal=20 and 18 active connections and 1 idle connection would trigger removeAbandonedOnBorrow, but only the active connections that aren't used for more then "removeAbandonedTimeout" seconds are removed (default 300 sec). Traversing a resultset doesn't count as being used. Creating a Statement, PreparedStatement or CallableStatement or using one of these to execute a query (using one of the execute methods) resets the lastUsed property of the parent connection. |
||
3-2-2 C3P0 屬性說明表
| 屬性(Parameter) |
預設值(Default) |
描述(Description) |
| user |
|
同DBCP中的username屬性 |
| password |
|
同DBCP中的password屬性 |
| jdbcUrl |
|
同DBCP中的jdbcUrl屬性 |
| driverClass |
|
同DBCP中的driverClass屬性 |
| autoCommitOnClose |
false |
預設值false表示回滾任何未提交的任務,設定為true則全部提交,而不是在關閉連線之前回滾 (C3P0's default policy is to rollback any uncommitted, pending work. Setting autoCommitOnClose to true causes uncommitted pending work to be committed, rather than rolled back on Connection close.) *參見DBCP中的defaultAutoCommit屬性 |
| initialPoolSize |
3 |
初始化連線:連線池啟動時建立的初始化連線數量(The initial number of connections that are created when the pool is started. *參見DBCP中的initialSize屬性 |
| maxPoolSize |
15 |
連線池中保留的最大連線數(Maximum number of Connections a pool will maintain at any given time.) *參見DBCP中的maxIdle屬性 |
| minPoolSize |
3 |
連線池中保留的最小連線數(Minimum number of Connections a pool will maintain at any given time.) *參見DBCP中的maxIdle屬性 |
| maxIdleTime |
0 |
最大等待時間:當沒有可用連線時,連線池等待連線被歸還的最大時間(以秒計數),超過時間則丟擲異常,如果設定為0表示無限等待(Seconds a Connection can remain pooled but unused before being discarded. Zero means idle connections never expire.) *參見DBCP中maxWaitMillis 屬性 |
| preferredTestQuery |
null |
定義所有連線測試都執行的測試語句。在使用連線測試的情況下這個一顯著提高測試速度。注意：測試的表必須在初始資料來源的時候就存在。(Defines the query that will be executed for all connection tests, if the default ConnectionTester (or some other implementation of QueryConnectionTester, or better yet FullQueryConnectionTester) is being used. Defining a preferredTestQuery that will execute quickly in your database may dramatically speed up Connection tests.) |
| testConnectionOn- Checkin |
false |
如果設為true那麼在取得連線的同時將校驗連線的有效性。(If true, an operation will be performed asynchronously at every connection checkin to verify that the connection is valid. Use in combination with idleConnectionTestPeriod for quite reliable, always asynchronous Connection testing.) *參見DBCP中的testOnBorrow屬性 |
| testConnectionOn- Checkout |
false |
如果設為true那麼在每個connection提交的時候都將校驗其有效性,但是要確保配置的preferredTestQuery的有效性(If true, an operation will be performed at every connection checkout to verify that the connection is valid. Be sure to set an efficient preferredTestQuery or automaticTestTable if you set this to true.) *參見DBCP中的testOnBorrow屬性 |
| idleConnectionTest- Period |
0 |
如果設定大於0,表示過了多少秒檢查一次空閒連線,結合testConnectionOnCheckin以及testConnectionOnCheckout使用(If this is a number greater than 0, c3p0 will test all idle, pooled but unchecked-out connections, every this number of seconds.) |
| acquireRetryAttempts |
30 |
定義在從資料庫獲取新連線失敗後重復嘗試的次數, 如果小於0則表示無限制的連線。(Defines how many times c3p0 will try to acquire a new Connection from the database before giving up. If this value is less than or equal to zero, c3p0 will keep trying to fetch a Connection indefinitely.) |
| acquireRetryDelay |
1000 |
兩次連線中的間隔時間，單位毫秒。(Milliseconds, time c3p0 will wait between acquire attempts.) |
| breakAfterAcquire- Failure |
false |
獲取連線失敗將會引起所有等待連線池來獲取連線的執行緒丟擲異常。但是資料來源仍有效保留，並在下次呼叫 getConnection() 的時候繼續嘗試獲取連線。如果為 true，那麼在嘗試獲取連線失敗後該資料來源將宣告已斷開並永久關閉。(If true, a pooled DataSource will declare itself broken and be permanently closed if a Connection cannot be obtained from the database after making acquireRetryAttempts to acquire one. If false, failure to obtain a Connection will cause all Threads waiting for the pool to acquire a Connection to throw an Exception, but the DataSource will remain valid, and will attempt to acquire again following a call to getConnection().) |
| checkoutTimeout |
0 |
當連線池用完時客戶端呼叫 getConnection() 後等待獲取新連線的時間，潮溼後將丟擲SQLException，如設為0，則為無限期等待。單位毫秒。(The number of milliseconds a client calling getConnection() will wait for a Connection to be checked-in or acquired when the pool is exhausted. Zero means wait indefinitely. Setting any positive value will cause the getConnection() call to time-out and break with an SQLException after the specified number of milliseconds.) |
| maxStatements |
0 |
控制資料來源內載入的PreparedStatements數量(Enable prepared statement pooling for this pool.) |
| maxStatementsPer- Connection |
0 |
定義了連線池內單個連線所擁有的最大快取statements數(The maximum number of open statements that can be allocated from the statement pool at the same time, or negative for no limit.) |
3-2-3 DRUID 屬性說明表
| 屬性(Parameter) |
預設值(Default) |
描述(Description) |
| username |
|
連線資料庫的使用者名稱 |
| password |
|
連線資料庫的密碼 |
| jdbcUrl |
|
同DBCP中的jdbcUrl屬性 |
| driverClassName |
根據url自動識別 |
這一項可配可不配，如果不配置druid會根據url自動識別dbType，然後選擇相應的driverClassName |
| initialSize |
0 |
初始化時建立物理連線的個數。初始化發生在顯示呼叫init方法，或者第一次getConnection時 *參見DBCP中的initialSize屬性 |
| maxActive |
8 |
最大連線池數量(Maximum number of Connections a pool will maintain at any given time.) *參見DBCP中的maxTotal屬性 |
| maxIdle |
8 |
已經不再使用，配置了也沒效果 *參見DBCP中的maxIdle屬性 |
| minIdle |
|
最小連線池數量 |
| maxWait |
|
獲取連線時最大等待時間，單位毫秒。配置了maxWait之後，預設啟用公平鎖，併發效率會有所下降，如果需要可以通過配置useUnfairLock屬性為true使用非公平鎖。 |
| poolPreparedState- ments |
false |
是否快取preparedStatement，也就是PSCache。PSCache對支援遊標的資料庫效能提升巨大，比如說oracle。 |
| maxOpenPrepared- Statements |
-1 |
要啟用PSCache，必須配置大於0，當大於0時，poolPreparedStatements自動觸發修改為true。 在Druid中，不會存在Oracle下PSCache佔用記憶體過多的問題，可以把這個數值配置大一些，比如說100 |
| testOnBorrow |
true |
申請連線時執行validationQuery檢測連線是否有效，做了這個配置會降低效能。 |
| testOnReturn |
false |
歸還連線時執行validationQuery檢測連線是否有效，做了這個配置會降低效能 |
| testWhileIdle |
false |
建議配置為true，不影響效能，並且保證安全性。申請連線的時候檢測，如果空閒時間大於timeBetweenEvictionRunsMillis，執行validationQuery檢測連線是否有效。 |
| validationQuery |
|
用來檢測連線是否有效的sql，要求是一個查詢語句。如果validationQuery為null，testOnBorrow、testOnReturn、testWhileIdle都不會其作用。在mysql中通常為select 'x'，在oracle中通常為select 1 from dual |
| timeBetweenEviction-RunsMillis |
|
1) Destroy執行緒會檢測連線的間隔時間 2) testWhileIdle的判斷依據 |
| minEvictableIdle- TimeMillis |
|
Destory執行緒中如果檢測到當前連線的最後活躍時間和當前時間的差值大於minEvictableIdleTimeMillis，則關閉當前連線。 |
| removeAbandoned |
|
對於建立時間超過removeAbandonedTimeout的連線強制關閉 |
| removeAbandoned-Timeout |
|
指定連線建立多長時間就需要被強制關閉 |
| logAbandoned |
false |
指定發生removeabandoned的時候，是否記錄當前執行緒的堆疊資訊到日誌中 |
| filters |
|
屬性型別是字串，通過別名的方式配置擴充套件外掛，常用的外掛有： 1）監控統計用的filter:stat 2）日誌用的filter:log4j 3）防禦sql注入的filter:wall |