org.springframework.jdbc.datasource.LazyConnectionDataSourceProxy Maven / Gradle / Ivy
/*
* Copyright 2002-2020 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.jdbc.datasource;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.sql.DataSource;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.core.Constants;
import org.springframework.lang.Nullable;
/**
* Proxy for a target DataSource, fetching actual JDBC Connections lazily,
* i.e. not until first creation of a Statement. Connection initialization
* properties like auto-commit mode, transaction isolation and read-only mode
* will be kept and applied to the actual JDBC Connection as soon as an
* actual Connection is fetched (if ever). Consequently, commit and rollback
* calls will be ignored if no Statements have been created.
*
* This DataSource proxy allows to avoid fetching JDBC Connections from
* a pool unless actually necessary. JDBC transaction control can happen
* without fetching a Connection from the pool or communicating with the
* database; this will be done lazily on first creation of a JDBC Statement.
*
*
If you configure both a LazyConnectionDataSourceProxy and a
* TransactionAwareDataSourceProxy, make sure that the latter is the outermost
* DataSource. In such a scenario, data access code will talk to the
* transaction-aware DataSource, which will in turn work with the
* LazyConnectionDataSourceProxy.
*
*
Lazy fetching of physical JDBC Connections is particularly beneficial
* in a generic transaction demarcation environment. It allows you to demarcate
* transactions on all methods that could potentially perform data access,
* without paying a performance penalty if no actual data access happens.
*
*
This DataSource proxy gives you behavior analogous to JTA and a
* transactional JNDI DataSource (as provided by the Java EE server), even
* with a local transaction strategy like DataSourceTransactionManager or
* HibernateTransactionManager. It does not add value with Spring's
* JtaTransactionManager as transaction strategy.
*
*
Lazy fetching of JDBC Connections is also recommended for read-only
* operations with Hibernate, in particular if the chances of resolving the
* result in the second-level cache are high. This avoids the need to
* communicate with the database at all for such read-only operations.
* You will get the same effect with non-transactional reads, but lazy fetching
* of JDBC Connections allows you to still perform reads in transactions.
*
*
NOTE: This DataSource proxy needs to return wrapped Connections
* (which implement the {@link ConnectionProxy} interface) in order to handle
* lazy fetching of an actual JDBC Connection. Use {@link Connection#unwrap}
* to retrieve the native JDBC Connection.
*
* @author Juergen Hoeller
* @since 1.1.4
* @see DataSourceTransactionManager
*/
public class LazyConnectionDataSourceProxy extends DelegatingDataSource {
/** Constants instance for TransactionDefinition. */
private static final Constants constants = new Constants(Connection.class);
private static final Log logger = LogFactory.getLog(LazyConnectionDataSourceProxy.class);
@Nullable
private Boolean defaultAutoCommit;
@Nullable
private Integer defaultTransactionIsolation;
/**
* Create a new LazyConnectionDataSourceProxy.
* @see #setTargetDataSource
*/
public LazyConnectionDataSourceProxy() {
}
/**
* Create a new LazyConnectionDataSourceProxy.
* @param targetDataSource the target DataSource
*/
public LazyConnectionDataSourceProxy(DataSource targetDataSource) {
setTargetDataSource(targetDataSource);
afterPropertiesSet();
}
/**
* Set the default auto-commit mode to expose when no target Connection
* has been fetched yet (when the actual JDBC Connection default is not known yet).
*
If not specified, the default gets determined by checking a target
* Connection on startup. If that check fails, the default will be determined
* lazily on first access of a Connection.
* @see java.sql.Connection#setAutoCommit
*/
public void setDefaultAutoCommit(boolean defaultAutoCommit) {
this.defaultAutoCommit = defaultAutoCommit;
}
/**
* Set the default transaction isolation level to expose when no target Connection
* has been fetched yet (when the actual JDBC Connection default is not known yet).
*
This property accepts the int constant value (e.g. 8) as defined in the
* {@link java.sql.Connection} interface; it is mainly intended for programmatic
* use. Consider using the "defaultTransactionIsolationName" property for setting
* the value by name (e.g. "TRANSACTION_SERIALIZABLE").
*
If not specified, the default gets determined by checking a target
* Connection on startup. If that check fails, the default will be determined
* lazily on first access of a Connection.
* @see #setDefaultTransactionIsolationName
* @see java.sql.Connection#setTransactionIsolation
*/
public void setDefaultTransactionIsolation(int defaultTransactionIsolation) {
this.defaultTransactionIsolation = defaultTransactionIsolation;
}
/**
* Set the default transaction isolation level by the name of the corresponding
* constant in {@link java.sql.Connection}, e.g. "TRANSACTION_SERIALIZABLE".
* @param constantName name of the constant
* @see #setDefaultTransactionIsolation
* @see java.sql.Connection#TRANSACTION_READ_UNCOMMITTED
* @see java.sql.Connection#TRANSACTION_READ_COMMITTED
* @see java.sql.Connection#TRANSACTION_REPEATABLE_READ
* @see java.sql.Connection#TRANSACTION_SERIALIZABLE
*/
public void setDefaultTransactionIsolationName(String constantName) {
setDefaultTransactionIsolation(constants.asNumber(constantName).intValue());
}
@Override
public void afterPropertiesSet() {
super.afterPropertiesSet();
// Determine default auto-commit and transaction isolation
// via a Connection from the target DataSource, if possible.
if (this.defaultAutoCommit == null || this.defaultTransactionIsolation == null) {
try {
try (Connection con = obtainTargetDataSource().getConnection()) {
checkDefaultConnectionProperties(con);
}
}
catch (SQLException ex) {
logger.debug("Could not retrieve default auto-commit and transaction isolation settings", ex);
}
}
}
/**
* Check the default connection properties (auto-commit, transaction isolation),
* keeping them to be able to expose them correctly without fetching an actual
* JDBC Connection from the target DataSource.
*
This will be invoked once on startup, but also for each retrieval of a
* target Connection. If the check failed on startup (because the database was
* down), we'll lazily retrieve those settings.
* @param con the Connection to use for checking
* @throws SQLException if thrown by Connection methods
*/
protected synchronized void checkDefaultConnectionProperties(Connection con) throws SQLException {
if (this.defaultAutoCommit == null) {
this.defaultAutoCommit = con.getAutoCommit();
}
if (this.defaultTransactionIsolation == null) {
this.defaultTransactionIsolation = con.getTransactionIsolation();
}
}
/**
* Expose the default auto-commit value.
*/
@Nullable
protected Boolean defaultAutoCommit() {
return this.defaultAutoCommit;
}
/**
* Expose the default transaction isolation value.
*/
@Nullable
protected Integer defaultTransactionIsolation() {
return this.defaultTransactionIsolation;
}
/**
* Return a Connection handle that lazily fetches an actual JDBC Connection
* when asked for a Statement (or PreparedStatement or CallableStatement).
*
The returned Connection handle implements the ConnectionProxy interface,
* allowing to retrieve the underlying target Connection.
* @return a lazy Connection handle
* @see ConnectionProxy#getTargetConnection()
*/
@Override
public Connection getConnection() throws SQLException {
return (Connection) Proxy.newProxyInstance(
ConnectionProxy.class.getClassLoader(),
new Class[] {ConnectionProxy.class},
new LazyConnectionInvocationHandler());
}
/**
* Return a Connection handle that lazily fetches an actual JDBC Connection
* when asked for a Statement (or PreparedStatement or CallableStatement).
*
The returned Connection handle implements the ConnectionProxy interface,
* allowing to retrieve the underlying target Connection.
* @param username the per-Connection username
* @param password the per-Connection password
* @return a lazy Connection handle
* @see ConnectionProxy#getTargetConnection()
*/
@Override
public Connection getConnection(String username, String password) throws SQLException {
return (Connection) Proxy.newProxyInstance(
ConnectionProxy.class.getClassLoader(),
new Class[] {ConnectionProxy.class},
new LazyConnectionInvocationHandler(username, password));
}
/**
* Invocation handler that defers fetching an actual JDBC Connection
* until first creation of a Statement.
*/
private class LazyConnectionInvocationHandler implements InvocationHandler {
@Nullable
private String username;
@Nullable
private String password;
@Nullable
private Boolean autoCommit;
@Nullable
private Integer transactionIsolation;
private boolean readOnly = false;
private int holdability = ResultSet.CLOSE_CURSORS_AT_COMMIT;
private boolean closed = false;
@Nullable
private Connection target;
public LazyConnectionInvocationHandler() {
this.autoCommit = defaultAutoCommit();
this.transactionIsolation = defaultTransactionIsolation();
}
public LazyConnectionInvocationHandler(String username, String password) {
this();
this.username = username;
this.password = password;
}
@Override
@Nullable
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// Invocation on ConnectionProxy interface coming in...
switch (method.getName()) {
case "equals":
// We must avoid fetching a target Connection for "equals".
// Only consider equal when proxies are identical.
return (proxy == args[0]);
case "hashCode":
// We must avoid fetching a target Connection for "hashCode",
// and we must return the same hash code even when the target
// Connection has been fetched: use hashCode of Connection proxy.
return System.identityHashCode(proxy);
case "getTargetConnection":
// Handle getTargetConnection method: return underlying connection.
return getTargetConnection(method);
case "unwrap":
if (((Class) args[0]).isInstance(proxy)) {
return proxy;
}
break;
case "isWrapperFor":
if (((Class) args[0]).isInstance(proxy)) {
return true;
}
break;
}
if (!hasTargetConnection()) {
// No physical target Connection kept yet ->
// resolve transaction demarcation methods without fetching
// a physical JDBC Connection until absolutely necessary.
switch (method.getName()) {
case "toString":
return "Lazy Connection proxy for target DataSource [" + getTargetDataSource() + "]";
case "getAutoCommit":
if (this.autoCommit != null) {
return this.autoCommit;
}
// Else fetch actual Connection and check there,
// because we didn't have a default specified.
break;
case "setAutoCommit":
this.autoCommit = (Boolean) args[0];
return null;
case "getTransactionIsolation":
if (this.transactionIsolation != null) {
return this.transactionIsolation;
}
// Else fetch actual Connection and check there,
// because we didn't have a default specified.
break;
case "setTransactionIsolation":
this.transactionIsolation = (Integer) args[0];
return null;
case "isReadOnly":
return this.readOnly;
case "setReadOnly":
this.readOnly = (Boolean) args[0];
return null;
case "getHoldability":
return this.holdability;
case "setHoldability":
this.holdability = (Integer) args[0];
return null;
case "commit":
case "rollback":
// Ignore: no statements created yet.
return null;
case "getWarnings":
case "clearWarnings":
// Ignore: no warnings to expose yet.
return null;
case "close":
// Ignore: no target connection yet.
this.closed = true;
return null;
case "isClosed":
return this.closed;
default:
if (this.closed) {
// Connection proxy closed, without ever having fetched a
// physical JDBC Connection: throw corresponding SQLException.
throw new SQLException("Illegal operation: connection is closed");
}
}
}
// Target Connection already fetched,
// or target Connection necessary for current operation ->
// invoke method on target connection.
try {
return method.invoke(getTargetConnection(method), args);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}
/**
* Return whether the proxy currently holds a target Connection.
*/
private boolean hasTargetConnection() {
return (this.target != null);
}
/**
* Return the target Connection, fetching it and initializing it if necessary.
*/
private Connection getTargetConnection(Method operation) throws SQLException {
if (this.target == null) {
// No target Connection held -> fetch one.
if (logger.isTraceEnabled()) {
logger.trace("Connecting to database for operation '" + operation.getName() + "'");
}
// Fetch physical Connection from DataSource.
this.target = (this.username != null) ?
obtainTargetDataSource().getConnection(this.username, this.password) :
obtainTargetDataSource().getConnection();
// If we still lack default connection properties, check them now.
checkDefaultConnectionProperties(this.target);
// Apply kept transaction settings, if any.
if (this.readOnly) {
try {
this.target.setReadOnly(true);
}
catch (Exception ex) {
// "read-only not supported" -> ignore, it's just a hint anyway
logger.debug("Could not set JDBC Connection read-only", ex);
}
}
if (this.transactionIsolation != null &&
!this.transactionIsolation.equals(defaultTransactionIsolation())) {
this.target.setTransactionIsolation(this.transactionIsolation);
}
if (this.autoCommit != null && this.autoCommit != this.target.getAutoCommit()) {
this.target.setAutoCommit(this.autoCommit);
}
}
else {
// Target Connection already held -> return it.
if (logger.isTraceEnabled()) {
logger.trace("Using existing database connection for operation '" + operation.getName() + "'");
}
}
return this.target;
}
}
}