org.springframework.integration.handler.ExpressionEvaluatingMessageProcessor.java Source code

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Here is the source code for org.springframework.integration.handler.ExpressionEvaluatingMessageProcessor.java

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/*
 * Copyright 2002-2019 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.integration.handler;

import org.springframework.expression.Expression;
import org.springframework.expression.ParseException;
import org.springframework.lang.Nullable;
import org.springframework.messaging.Message;
import org.springframework.util.Assert;

/**
 * A {@link MessageProcessor} implementation that evaluates a SpEL expression
 * with the Message itself as the root object within the evaluation context.
 *
 * @author Mark Fisher
 * @author Artem Bilan
 * @author Gary Russell
 *
 * @since 2.0
 */
public class ExpressionEvaluatingMessageProcessor<T> extends AbstractMessageProcessor<T> {

    private final Expression expression;

    private final Class<T> expectedType;

    /**
     * Create an {@link ExpressionEvaluatingMessageProcessor} for the given expression.
     * @param expression The expression.
     */
    public ExpressionEvaluatingMessageProcessor(Expression expression) {
        this(expression, null);
    }

    /**
     * Create an {@link ExpressionEvaluatingMessageProcessor} for the given expression
     * and expected type for its evaluation result.
     * @param expression The expression.
     * @param expectedType The expected type.
     */
    public ExpressionEvaluatingMessageProcessor(Expression expression, @Nullable Class<T> expectedType) {
        Assert.notNull(expression, "The expression must not be null");
        try {
            this.expression = expression;
            this.expectedType = expectedType;
        } catch (ParseException e) {
            throw new IllegalArgumentException("Failed to parse expression.", e);
        }
    }

    /**
     * Create an {@link ExpressionEvaluatingMessageProcessor} for the given expression.
     * @param expression a SpEL expression to evaluate.
     * @since 5.0
     */
    public ExpressionEvaluatingMessageProcessor(String expression) {
        try {
            this.expression = EXPRESSION_PARSER.parseExpression(expression);
            this.expectedType = null;
        } catch (ParseException e) {
            throw new IllegalArgumentException("Failed to parse expression.", e);
        }
    }

    /**
     * Construct {@link ExpressionEvaluatingMessageProcessor} for the provided
     * SpEL expression and expected result type.
     * @param expression a SpEL expression to evaluate.
     * @param expectedType the expected result type.
     * @since 5.0
     */
    public ExpressionEvaluatingMessageProcessor(String expression, @Nullable Class<T> expectedType) {
        try {
            this.expression = EXPRESSION_PARSER.parseExpression(expression);
            this.expectedType = expectedType;
        } catch (ParseException e) {
            throw new IllegalArgumentException("Failed to parse expression.", e);
        }
    }

    /**
     * Processes the Message by evaluating the expression with that Message as the
     * root object. The expression evaluation result Object will be returned.
     * @param message The message.
     * @return The result of processing the message.
     */
    @Override
    public T processMessage(Message<?> message) {
        return evaluateExpression(this.expression, message, this.expectedType);
    }

    @Override
    public String toString() {
        return "ExpressionEvaluatingMessageProcessor for: [" + this.expression.getExpressionString() + "]";
    }

}