Why FastJSON Lost the amount Field After JDK 11 Upgrade – A Deep Dive

Background

After upgrading the service to JDK 11, class loading order changed, causing different classes to be loaded from multiple JARs, which affected FastJSON serialization results.

Symptoms

Customer reports that the order page cannot initiate a dispute and errors occur.

Resolution Process

Rollback deployed version in two batches of 30 machines, restored service within 6 minutes.

Investigation Steps

Checked JVM parameters, occupied ports, sandbox‑agent plugin, Spring Boot version, and FastJSON configuration.

new SpringApplicationBuilder(DestinyApplication.class)
    .web(WebApplicationType.NONE) // specify non‑web application
    .profiles(DiamondProfiles.load())
    .run(args);

The line .web(WebApplicationType.NONE) interfered with port handling.

@Controller
public static class OkController {
    @ResponseBody
    @RequestMapping("/ok.jsp")
    public String ok() { return "success"; }

    @GetMapping("/checkpreload.htm")
    public @ResponseBody String checkPreload() { return "success"; }
}

Added a configuration to exclude health‑check paths:

icbusession.authorization.exclude-paths=/favicon.ico,/checkpreload.htm,/status.taobao,/ok.jsp

FastJSON Analysis

The issue was traced to FastJSON deserialization of the Money class where the derived amount field was lost on the production machine.

public class Money implements Serializable, Comparable {
    private long cent;
    private Currency currency;
    private String currencyCode;
    public BigDecimal getAmount() {
        return BigDecimal.valueOf(cent, currency.getDefaultFractionDigits());
    }
    public void setAmount(BigDecimal amount) {
        if (amount != null) {
            cent = rounding(amount.movePointRight(2), BigDecimal.ROUND_HALF_EVEN);
        }
    }
}

FastJSON reads getter/setter methods; the production JAR lacked the setAmount method because a custom jar overwrote the class, causing the amount to be zero.

Final Fix

Removed the conflicting custom jar from the dependency tree, which restored proper deserialization of the amount field.