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Adds a sample implementation for a JDBC subscribable channel using Postres LISTEN/NOTIFY.
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‎build.gradle‎

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@@ -713,6 +713,7 @@ project('spring-integration-jdbc') {
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dependencies {
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api project(':spring-integration-core')
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api 'org.springframework:spring-jdbc'
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compileOnly "org.postgresql:postgresql:$postgresVersion"
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testImplementation "com.h2database:h2:$h2Version"
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testImplementation "org.hsqldb:hsqldb:$hsqldbVersion"

‎spring-integration-jdbc/src/main/java/org/springframework/integration/jdbc/channel/PgConnectionSupplier.java‎

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package org.springframework.integration.jdbc.channel;
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import org.postgresql.jdbc.PgConnection;
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import java.sql.SQLException;
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@FunctionalInterface
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public interface PgConnectionSupplier {
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PgConnection get() throws SQLException;
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}

‎spring-integration-jdbc/src/main/java/org/springframework/integration/jdbc/channel/PostgresChannelMessageTableSubscriber.java‎

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package org.springframework.integration.jdbc.channel;
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import org.postgresql.PGNotification;
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import org.postgresql.jdbc.PgConnection;
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import org.springframework.context.SmartLifecycle;
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import org.springframework.core.log.LogAccessor;
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import org.springframework.integration.jdbc.store.JdbcChannelMessageStore;
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import org.springframework.integration.util.UUIDConverter;
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import org.springframework.util.Assert;
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import java.sql.Statement;
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import java.util.Map;
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import java.util.Set;
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import java.util.concurrent.ConcurrentHashMap;
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import java.util.concurrent.Executor;
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import java.util.concurrent.Executors;
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import java.util.concurrent.atomic.AtomicBoolean;
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public class PostgresChannelMessageTableSubscriber implements SmartLifecycle {
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private final LogAccessor logger = new LogAccessor(this.getClass()); // NOSONAR final
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private final PgConnectionSupplier connectionSupplier;
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private final Executor executor;
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private final String tablePrefix;
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private final AtomicBoolean running = new AtomicBoolean();
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private volatile Object identity;
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private final Map<String, Set<PostgresChannelMessageTableSubscription>> subscriptions = new ConcurrentHashMap<>();
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public PostgresChannelMessageTableSubscriber(PgConnectionSupplier connectionSupplier) {
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this(connectionSupplier, JdbcChannelMessageStore.DEFAULT_TABLE_PREFIX);
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}
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public PostgresChannelMessageTableSubscriber(PgConnectionSupplier connectionSupplier, String tablePrefix) {
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this(connectionSupplier, Executors.newSingleThreadExecutor(job -> {
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Thread t = new Thread(job);
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t.setDaemon(true);
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t.setName("");
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return t;
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}), tablePrefix);
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}
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public PostgresChannelMessageTableSubscriber(PgConnectionSupplier connectionSupplier, Executor executor) {
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this(connectionSupplier, executor, JdbcChannelMessageStore.DEFAULT_TABLE_PREFIX);
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}
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public PostgresChannelMessageTableSubscriber(PgConnectionSupplier connectionSupplier, Executor executor, String tablePrefix) {
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Assert.notNull(connectionSupplier, "A connectionSupplier must be provided.");
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Assert.notNull(executor, "A executor must be provided.");
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Assert.notNull(tablePrefix, "A table prefix must be set.");
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this.connectionSupplier = connectionSupplier;
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this.executor = executor;
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this.tablePrefix = tablePrefix;
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}
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public boolean subscribe(PostgresChannelMessageTableSubscription subscription) {
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Set<PostgresChannelMessageTableSubscription> subscriptions = this.subscriptions.computeIfAbsent(getKey(subscription.getGroupId()) + subscription.getRegion(), ignored -> ConcurrentHashMap.newKeySet());
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return subscriptions.add(subscription);
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}
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public boolean unsubscribe(PostgresChannelMessageTableSubscription subscription) {
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Set<PostgresChannelMessageTableSubscription> subscriptions = this.subscriptions.get(getKey(subscription.getGroupId()) + subscription.getRegion());
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return subscriptions != null && subscriptions.remove(subscription);
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}
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@Override
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public void start() {
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if (running.getAndSet(true)) {
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return;
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}
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// Avoid that stop/start sequence reactivates previously stopped thread.
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Object current = new Object();
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identity = current;
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executor.execute(() -> {
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try {
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while (isActive(current)) {
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try {
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PgConnection conn = this.connectionSupplier.get();
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try (Statement stmt = conn.createStatement()) {
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stmt.execute("LISTEN " + this.tablePrefix.toLowerCase() + "channel_message_notify");
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} catch (Throwable t) {
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try {
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conn.close();
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} catch (Throwable suppressed) {
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t.addSuppressed(suppressed);
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}
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throw t;
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}
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try {
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while (isActive(current)) {
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PGNotification[] notifications = conn.getNotifications(0);
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// Unfortunately, there is no good way of interrupting a notification poll.
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if (!isActive(current)) {
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return;
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}
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if (notifications != null) {
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for (PGNotification notification : notifications) {
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String parameter = notification.getParameter();
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Set<PostgresChannelMessageTableSubscription> subscriptions = this.subscriptions.get(parameter);
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if (subscriptions == null) {
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continue;
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}
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for (PostgresChannelMessageTableSubscription subscription : subscriptions) {
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subscription.onPossibleUpdate();
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}
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}
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}
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}
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} finally {
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conn.close();
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}
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} catch (Exception e) {
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// The getNotifications method does not throw a meaningful message on interruption.
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// Therefore, we do not log an error, unless it occurred while active.
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if (isActive(current)) {
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logger.error(e, "Failed to poll notifications from Postgres database");
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}
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} catch (Throwable t) {
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logger.error(t, "Failed to poll notifications from Postgres database");
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return;
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}
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}
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} finally {
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running.set(false);
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}
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});
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}
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private boolean isActive(Object identity) {
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if (identity != this.identity) {
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return false;
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} else if (!running.get()) {
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return false;
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} else if (Thread.interrupted()) {
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running.set(false);
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return false;
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} else {
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return true;
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}
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}
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@Override
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public void stop() {
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running.set(false);
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}
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@Override
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public boolean isRunning() {
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return running.get();
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}
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private String getKey(Object input) {
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return input == null ? null : UUIDConverter.getUUID(input).toString();
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}
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}

‎spring-integration-jdbc/src/main/java/org/springframework/integration/jdbc/channel/PostgresChannelMessageTableSubscription.java‎

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package org.springframework.integration.jdbc.channel;
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import org.springframework.integration.jdbc.store.JdbcChannelMessageStore;
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import org.springframework.messaging.Message;
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import org.springframework.messaging.MessageHandler;
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public final class PostgresChannelMessageTableSubscription {
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private final Object groupId;
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private final String region;
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private final Runnable onPossibleUpdate;
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public PostgresChannelMessageTableSubscription(Object groupId, Runnable onPossibleUpdate) {
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this(groupId, JdbcChannelMessageStore.DEFAULT_REGION, onPossibleUpdate);
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}
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public PostgresChannelMessageTableSubscription(Object groupId, String region, Runnable onPossibleUpdate) {
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this.groupId = groupId;
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this.region = region;
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this.onPossibleUpdate = onPossibleUpdate;
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}
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public Object getGroupId() {
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return groupId;
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}
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public String getRegion() {
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return region;
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}
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public void onPossibleUpdate() {
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onPossibleUpdate.run();
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}
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public static PostgresChannelMessageTableSubscription ofMessageStore(JdbcChannelMessageStore messageStore,
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Object groupId,
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MessageHandler handler) {
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return new PostgresChannelMessageTableSubscription(groupId, messageStore.getRegion(), () -> {
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Message<?> message = messageStore.pollMessageFromGroup(groupId);
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while (message != null) {
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handler.handleMessage(message);
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message = messageStore.pollMessageFromGroup(groupId);
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}
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});
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}
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}

‎spring-integration-jdbc/src/main/java/org/springframework/integration/jdbc/store/JdbcChannelMessageStore.java‎

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@@ -273,6 +273,14 @@ public void setRegion(String region) {
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this.region = region;
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}
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/**
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* Returns the current region that was set or {@link #DEFAULT_REGION}, which is the default.
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* @return the set region name
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*/
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public String getRegion() {
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return region;
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}
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/**
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* A converter for serializing messages to byte arrays for storage.
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* @param serializer The serializer to set

‎spring-integration-jdbc/src/main/resources/org/springframework/integration/jdbc/schema-postgresql.sql‎

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@@ -58,3 +58,19 @@ CREATE TABLE INT_METADATA_STORE (
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REGION VARCHAR(100) NOT NULL,
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constraint INT_METADATA_STORE_PK primary key (METADATA_KEY, REGION)
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);
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-- This is only needed if using PostgresChannelMessageSubscriber
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-- CREATE FUNCTION INT_CHANNEL_MESSAGE_NOTIFY_FCT()
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-- RETURNS TRIGGER AS
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-- $BODY$
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-- BEGIN
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-- EXECUTE 'NOTIFY int_channel_message_notify, ''' || QUOTE_LITERAL(NEW.GROUP_KEY || NEW.REGION) || '''';
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-- RETURN NEW;
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-- END;
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-- $BODY$
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-- LANGUAGE PLPGSQL;
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--
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-- CREATE TRIGGER INT_CHANNEL_MESSAGE_NOTIFY_TRG
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-- AFTER INSERT ON INT_CHANNEL_MESSAGE
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-- FOR EACH ROW
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-- EXECUTE PROCEDURE INT_CHANNEL_MESSAGE_NOTIFY_FCT()

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