`MismatchedInputException` for nested repeating element name in `List`

[kaizen-horse]

I want to deserialize the string contents to Testclass.class on jackson 2.9.10
but I got a Exception: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of java.lang.String out of START_OBJECT token
at [Source: (StringReader); line: 11, column: 7] (through reference chain: saas.mall.supplier.zowoyoo.TestClass["prices"]->saas.mall.supplier.zowoyoo.TestClass$Prices["price"]->java.util.ArrayList[0]->saas.mall.supplier.zowoyoo.TestClass$Price["price"])

The Class that I want to deserialize contains a list of fields with the same name as the fields of the object in the list。

Here is the test case

    @Test
    public void testXml() throws IOException {
        String content = "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n" +
                "\n" +
                "<result>\n" +
                "  <prices>\n" +
                "    <price>\n" +
                "      <num>100</num>\n" +
                "      <price>7.0</price>\n" +
                "    </price>\n" +
                "  </prices>\n" +
                "</result>";
        com.fasterxml.jackson.dataformat.xml.XmlMapper xmlMapper =
                new com.fasterxml.jackson.dataformat.xml.XmlMapper();
        TestClass testClass = xmlMapper.readValue(content, TestClass.class);
        System.out.println(testClass);
    }

this is the Class I want to deserialize

package test;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlRootElement;

import java.util.ArrayList;
import java.util.List;


@JsonInclude(JsonInclude.Include.NON_NULL)
public class TestClass {
    /**
     *
     */
    private Prices prices = new Prices();

    public void setPrices(Prices prices) {
        this.prices = prices;
    }

    @JacksonXmlProperty(localName = "prices")
    public Prices getPrices() {
        return this.prices;
    }

    @JacksonXmlRootElement(localName = "price")
    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class Price {
        /**
         * 0.01
         */
        private String price;

        /**
         * 469
         */
        private String num;

        public void setPrice(String price) {
            this.price = price;
        }

        @JacksonXmlProperty(localName = "price")
        public String getPrice() {
            return this.price;
        }

        public void setNum(String num) {
            this.num = num;
        }

        @JacksonXmlProperty(localName = "num")
        public String getNum() {
            return this.num;
        }
    }

    @JacksonXmlRootElement(localName = "prices")
    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class Prices {
        /**
         *
         */
        private List<Price> price = new ArrayList<Price>();

        public void setPrice(List<Price> price) {
            this.price = price;
        }

        @JacksonXmlElementWrapper(useWrapping = false)
        @JacksonXmlProperty(localName = "price")
        public List<Price> getPrice() {
            return this.price;
        }
    }
}

PS: if I change the TestClass.Price.price‘s field type from String to Map,it works.like follwing

    @JacksonXmlRootElement(localName = "price")
    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class Price {
        /**
         * 0.01
         */
        private Map price;


        /**
         * 469
         */
        private String num;


        public void setPrice(Map price) {
            this.price = price;
        }

        @JacksonXmlProperty(localName="price")
        public Map getPrice(){
            return this.price;
        }

        public void setNum(String num) {
            this.num = num;
        }

        @JacksonXmlProperty(localName="num")
        public String getNum (){
            return this.num;
        }
    }

but when I use a string that contains more objects,
I got a exception：
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of java.util.LinkedHashMap (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('4.0')
at [Source: (StringReader); line: 11, column: 18] (through reference chain: test.TestClass["prices"]->test.TestClass$Prices["price"]->java.util.ArrayList[1]->test.TestClass$Price["price"])

    @Test
    public void testXml() throws IOException {
        String content = "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n" + "\n" +
            "<result>\n" + " <prices>\n" + " <price>\n" + " <num>100</num>\n" +
            " <price>7.0</price>\n" + " </price>\n" + " <price>\n" +
            " <num>100</num>\n" + " <price>4.0</price>\n" + " </price>" +
            " </prices>\n" + "</result>";
        com.fasterxml.jackson.dataformat.xml.XmlMapper xmlMapper = new com.fasterxml.jackson.dataformat.xml.XmlMapper();
        TestClass testClass = xmlMapper.readValue(content, TestClass.class);
        System.out.println(testClass);
    }

Hope to provide a solution，TKS

[lucanus81]

I have exactly the same issue. If your XML schema allows it, just try to change the name of one of the clashing names. If you cannot, then I think we need a fix.

[kaizen-horse]

I have exactly the same issue. If your XML schema allows it, just try to change the name of one of the clashing names. If you cannot, then I think we need a fix.

I couldn't find a solution and also my XML schema don't allows change the name, so I switched to DOM4J for deserialization,but It is complicate.A fix is better for me

[lucanus81]

Hi,
I think I found a solution. I have just discovered that for some weird/unknown reason, that

• "price" field (String) must be the first field in the "class Price", and even weirder,
• the xml you're trying to deserialise <price>123</price> must be the first tag.

In that example, I just had to change:

<price><num>123</num><price>123</price></price> to
<price><price>123</price><num>123</num></price>.

Notice that <price> must precede <num>. This must also be true in the class Price as well.

This is the full example:

    @JacksonXmlRootElement(localName = "price")
	@JsonIgnoreProperties(ignoreUnknown = true)
	@Data
	@NoArgsConstructor
	static class Price {
		private String price;
		private String num;
	}

	@JacksonXmlRootElement(localName = "prices")
	@JsonIgnoreProperties(ignoreUnknown = true)
	@NoArgsConstructor
	@Data
	static class Prices {
		@JacksonXmlElementWrapper(useWrapping = false)
		@JacksonXmlProperty(localName = "price")
		private List<Price> price = new ArrayList<Price>();
	}

	@JacksonXmlRootElement(localName = "result")
	@JsonIgnoreProperties(ignoreUnknown = true)
	@Data
	@NoArgsConstructor
	static class Result {
		private Prices prices;
	}

	@Test
	public void testXml() throws IOException {
		String content = "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n" + "\n"
				+ "<result>\n" 
				+ "<prices>\n"
				+ " <price>\n" + " <price>7.0</price>\n" + " <num>100</num>\n" + " </price>\n"
                            // As you see, I have changed the order of <price> and <num>:
				//+ " <price>\n" + " <num>100</num>\n" + " <price>7.0</price>\n" + " </price>\n" 
				+ " <price>\n" + " <price>4.0</price>\n" + " <num>100</num>\n" + " </price>" + " "
				+ "</prices>\n" 
				+ "</result>";
		Result testClass = mapper.readValue(content, Result.class);
		System.out.println(testClass);
		
		ByteArrayOutputStream output = new ByteArrayOutputStream();
		mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
		mapper.writeValue(output, testClass);
		System.out.println(output);
	}

Output:

XMLDeserializerTests.Result(prices=XMLDeserializerTests.Prices(price=[XMLDeserializerTests.Price(price=7.0, num=100), XMLDeserializerTests.Price(price=4.0, num=100)]))
<result>
  <prices>
    <price>
      <price>7.0</price>
      <num>100</num>
    </price>
    <price>
      <price>4.0</price>
      <num>100</num>
    </price>
  </prices>
</result>

I really hope this can help you somehow.

[cowtowncoder]

I hope to look into this soon, but one think I would suggest first is to use a newer version of Jackson: either 2.10.3 or newly released 2.11.0. Both have a few fixes beyond 2.9.10.

[lucanus81]

@cowtowncoder: I was using 2.10.2, but can reproduce the same issue on 2.11.0-RC1.

[cowtowncoder]

I can reproduce this, including some simplification. I can also see that if I first serialize structure, output matches input you'd expect (i.e. definition seems correct).
Don't yet know underlying reason although suspect it is due to mismatch for unwrapped-list handling, probably related to use of same name (price) in nested scope: that should be perfectly valid use, but perhaps something gets confused internally.

[kaizen-horse]

Hi,
I think I found a solution. I have just discovered that for some weird/unknown reason, that

• "price" field (String) must be the first field in the "class Price", and even weirder,
• the xml you're trying to deserialise <price>123</price> must be the first tag.

In that example, I just had to change:

• the xml you're trying to deserialise <price>123</price> must be the first tag.

the produce enviroment can't not change the xml message,so 'the xml you're trying to deserialise 123 must be the first tag.' I can't match this rule.Anyway, thanks a lot

[cowtowncoder]

@kaizenHorse I agree that this should not be necessary, but I think adding that note may be helpful for some users. But this issue should be resolved and I hope to do that once I have time to figure out exact root cause.

[kaizen-horse]

@kaizenHorse I agree that this should not be necessary, but I think adding that note may be helpful for some users. But this issue should be resolved and I hope to do that once I have time to figure out exact root cause.
ok,tks,I get the message,how can I add that note in a best way?

[cowtowncoder]

Hmmmh. Technically, I think this must be due to low-level detection of "wrapper-less" arrays, which creates virtual wrapper for databind to use. And in this case use of price at inner level too gets things confused. Wasn't caught before as names have been distinct.