线上代码对日志的记录，重要性自不必说。但是怎样记录日志也是有讲究的！

　　日志可以直接在每个方法中进行日志记录，优点是想怎么记就怎么记，缺点是记日志的代码可能会超过你的业务代码，可读性急剧下降，这也是日志框架蓬勃发展的源头。

　　日志也可以通过非业务代码侵入的形式进行记录，具体来说就是合作切面（aop）进行日志记录，好处自然是让业务更纯洁，缺点是运行性能会受到影响。

　　当然了，前面这些都不是本文的主题。本文的主题是，当你用切面进行日志记录时，然后fastjson是如何把你的业务代码给干掉的。

　　JsonObject.toJsonString(pj.getArgs()); 这是一个对入参的一个简单打印，至于使用fastjson的原因，自然是因为其输出字符的易读性。args是一个数组。那么这里会有什么问题？普通的参数自然是没有问题了。问题在于，fastjson转换对象为字符串时，报错了。为什么会这样？

　　注： 本文bug所现问题入参类型示例为：

public Object doSth(@RequestBody InBean in, HttpServletRequest request) {     // do sth...}

　　切面报错为：

public Object deal(ProceedingJoinPoint pjp) throws Throwable {      String argsStr = JSONObject.toJSONString(pjp.getArgs());      logger.info("入参:{}", argsStr);}

解析下fastjson源码过程：

初步进入源码：

// 直接调用json化方法    public static String toJSONString(Object object) {        return toJSONString(object, emptyFilters);    }    // 转到复杂参数的调用    public static String toJSONString(Object object, SerializeFilter[] filters, SerializerFeature... features) {        return toJSONString(object, SerializeConfig.globalInstance, filters, null, DEFAULT_GENERATE_FEATURE, features);    }    // 最终转换方法，1. 获取writer; 2. 处理filter; 3. 将数据定稿writer缓冲; 4. 返回缓冲数据给调用方    public static String toJSONString(Object object, //                                       SerializeConfig config, //                                       SerializeFilter[] filters, //                                       String dateFormat, //                                      int defaultFeatures, //                                       SerializerFeature... features) {        SerializeWriter out = new SerializeWriter(null, defaultFeatures, features);        try {            JSONSerializer serializer = new JSONSerializer(out, config);                        if (dateFormat != null && dateFormat.length() != 0) {                serializer.setDateFormat(dateFormat);                serializer.config(SerializerFeature.WriteDateUseDateFormat, true);            }            if (filters != null) {                for (SerializeFilter filter : filters) {                    serializer.addFilter(filter);                }            }            serializer.write(object);        // 最核心方法            return out.toString();        } finally {            out.close();        }    }

深入内部调用，追根究底：

// 写方法的进一步操作    public final void write(Object object) {        if (object == null) {            out.writeNull();            return;        }        Class
      clazz = object.getClass();        ObjectSerializer writer = getObjectWriter(clazz);    // 关键,返回各种对应的序列化器, 如 ObjectArrayCodec        try {            writer.write(this, object, null, null, 0);        // 调用对应的序列化器进行处理        } catch (IOException e) {            throw new JSONException(e.getMessage(), e);        }    }// 追踪到在运行write方法时出的问题 ObjectArrayCodec    public final void write(JSONSerializer serializer, Object object, Object fieldName, Type fieldType, int features)                                                                                                       throws IOException {        SerializeWriter out = serializer.out;        Object[] array = (Object[]) object;        if (object == null) {            out.writeNull(SerializerFeature.WriteNullListAsEmpty);            return;        }        int size = array.length;        int end = size - 1;        if (end == -1) {            out.append("[]");            return;        }        SerialContext context = serializer.context;        serializer.setContext(context, object, fieldName, 0);        try {            Class
      preClazz = null;            ObjectSerializer preWriter = null;            out.append('[');            if (out.isEnabled(SerializerFeature.PrettyFormat)) {                serializer.incrementIndent();                serializer.println();                for (int i = 0; i < size; ++i) {                    if (i != 0) {                        out.write(',');                        serializer.println();                    }                    serializer.write(array[i]);                }                serializer.decrementIdent();                serializer.println();                out.write(']');                return;            }            for (int i = 0; i < end; ++i) {                Object item = array[i];                if (item == null) {                    out.append("null,");                } else {                    if (serializer.containsReference(item)) {                        serializer.writeReference(item);                    } else {                        Class
      clazz = item.getClass();                        if (clazz == preClazz) {                            preWriter.write(serializer, item, null, null, 0);                        } else {                            preClazz = clazz;                            preWriter = serializer.getObjectWriter(clazz);                            preWriter.write(serializer, item, null, null, 0);                        }                    }                    out.append(',');                }            }            // 最后一个数组需要单独处理            Object item = array[end];            if (item == null) {                out.append("null]");            } else {                if (serializer.containsReference(item)) {                    serializer.writeReference(item);                } else {                    serializer.writeWithFieldName(item, end);                }                out.append(']');            }        } finally {            serializer.context = context;        }    }

找到最后个出现问题的地方，发现再往下无法再跟踪：

// 外部简单调用public final void writeWithFieldName(Object object, Object fieldName) {    writeWithFieldName(object, fieldName, null, 0);}// 最终报错是在这里    public final void writeWithFieldName(Object object, Object fieldName, Type fieldType, int fieldFeatures) {        try {            if (object == null) {                out.writeNull();                return;            }            Class
      clazz = object.getClass();            ObjectSerializer writer = getObjectWriter(clazz);        // ASMSerializer_2_RequestFacade             writer.write(this, object, fieldName, fieldType, fieldFeatures);    // 此处使用asm语言写的代码，无法debug, 但是会抛出 IllegalStateException         } catch (IOException e) {            throw new JSONException(e.getMessage(), e);        }    }

检查最后一次出现的问题，搜索出现的标记，找到动态生成asm代码的文件：

// 动态生成代码 ASMSerializer_2_RequestFacade    public JavaBeanSerializer createJavaBeanSerializer(SerializeBeanInfo beanInfo) throws Exception {        Class
       clazz = beanInfo.beanType;        if (clazz.isPrimitive()) {            throw new JSONException("unsupportd class " + clazz.getName());        }        JSONType jsonType = clazz.getAnnotation(JSONType.class);        FieldInfo[] unsortedGetters = beanInfo.fields;;        for (FieldInfo fieldInfo : unsortedGetters) {            if (fieldInfo.field == null //                && fieldInfo.method != null //                && fieldInfo.method.getDeclaringClass().isInterface()) {                return new JavaBeanSerializer(clazz);            }        }        FieldInfo[] getters = beanInfo.sortedFields;        boolean nativeSorted = beanInfo.sortedFields == beanInfo.fields;        if (getters.length > 256) {            return new JavaBeanSerializer(clazz);        }        for (FieldInfo getter : getters) {            if (!ASMUtils.checkName(getter.getMember().getName())) {                return new JavaBeanSerializer(clazz);            }        }        String className = "ASMSerializer_" + seed.incrementAndGet() + "_" + clazz.getSimpleName();        String packageName = ASMSerializerFactory.class.getPackage().getName();        String classNameType = packageName.replace('.', '/') + "/" + className;        String classNameFull = packageName + "." + className;        ClassWriter cw = new ClassWriter();        cw.visit(V1_5 //                 , ACC_PUBLIC + ACC_SUPER //                 , classNameType //                 , JavaBeanSerializer //                 , new String[] { ObjectSerializer } //        );        for (FieldInfo fieldInfo : getters) {            if (fieldInfo.fieldClass.isPrimitive() //                //|| fieldInfo.fieldClass.isEnum() //                || fieldInfo.fieldClass == String.class) {                continue;            }            new FieldWriter(cw, ACC_PUBLIC, fieldInfo.name + "_asm_fieldType", "Ljava/lang/reflect/Type;") //                                                                                                           .visitEnd();            if (List.class.isAssignableFrom(fieldInfo.fieldClass)) {                new FieldWriter(cw, ACC_PUBLIC, fieldInfo.name + "_asm_list_item_ser_",                                ObjectSerializer_desc) //                                                       .visitEnd();            }            new FieldWriter(cw, ACC_PUBLIC, fieldInfo.name + "_asm_ser_", ObjectSerializer_desc) //                                                                                                        .visitEnd();        }        MethodVisitor mw = new MethodWriter(cw, ACC_PUBLIC, "
      
       ", "(" + desc(SerializeBeanInfo.class) + ")V", null, null);        mw.visitVarInsn(ALOAD, 0);        mw.visitVarInsn(ALOAD, 1);        mw.visitMethodInsn(INVOKESPECIAL, JavaBeanSerializer, "
       
        ", "(" + desc(SerializeBeanInfo.class) + ")V");        // init _asm_fieldType        for (int i = 0; i < getters.length; ++i) {            FieldInfo fieldInfo = getters[i];            if (fieldInfo.fieldClass.isPrimitive() ////                || fieldInfo.fieldClass.isEnum() //                || fieldInfo.fieldClass == String.class) {                continue;            }            mw.visitVarInsn(ALOAD, 0);            if (fieldInfo.method != null) {                mw.visitLdcInsn(com.alibaba.fastjson.asm.Type.getType(desc(fieldInfo.declaringClass)));                mw.visitLdcInsn(fieldInfo.method.getName());                mw.visitMethodInsn(INVOKESTATIC, type(ASMUtils.class), "getMethodType",                                   "(Ljava/lang/Class;Ljava/lang/String;)Ljava/lang/reflect/Type;");            } else {                mw.visitVarInsn(ALOAD, 0);                mw.visitLdcInsn(i);                mw.visitMethodInsn(INVOKESPECIAL, JavaBeanSerializer, "getFieldType", "(I)Ljava/lang/reflect/Type;");            }            mw.visitFieldInsn(PUTFIELD, classNameType, fieldInfo.name + "_asm_fieldType", "Ljava/lang/reflect/Type;");        }        mw.visitInsn(RETURN);        mw.visitMaxs(4, 4);        mw.visitEnd();        boolean DisableCircularReferenceDetect = false;        if (jsonType != null) {            for (SerializerFeature featrues : jsonType.serialzeFeatures()) {                if (featrues == SerializerFeature.DisableCircularReferenceDetect) {                    DisableCircularReferenceDetect = true;                    break;                }            }        }        // 0 write        // 1 writeNormal        // 2 writeNonContext        for (int i = 0; i < 3; ++i) {            String methodName;            boolean nonContext = DisableCircularReferenceDetect;            boolean writeDirect = false;            if (i == 0) {                methodName = "write";                writeDirect = true;            } else if (i == 1) {                methodName = "writeNormal";            } else {                writeDirect = true;                nonContext = true;                methodName = "writeDirectNonContext";            }            Context context = new Context(getters, beanInfo, classNameType, writeDirect,                                          nonContext);            mw = new MethodWriter(cw, //                                  ACC_PUBLIC, //                                  methodName, //                                  "(L" + JSONSerializer                                              + ";Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/reflect/Type;I)V", //                                  null, //                                  new String[] { "java/io/IOException" } //            );            mw.visitVarInsn(ALOAD, Context.serializer);            mw.visitFieldInsn(GETFIELD, JSONSerializer, "out", SerializeWriter_desc);            mw.visitVarInsn(ASTORE, context.var("out"));            if ((!nativeSorted) //                && !context.writeDirect) {                if (jsonType == null || jsonType.alphabetic()) {                    Label _else = new Label();                    mw.visitVarInsn(ALOAD, context.var("out"));                    mw.visitMethodInsn(INVOKEVIRTUAL, SerializeWriter, "isSortField", "()Z");                    mw.visitJumpInsn(IFNE, _else);                    mw.visitVarInsn(ALOAD, 0);                    mw.visitVarInsn(ALOAD, 1);                    mw.visitVarInsn(ALOAD, 2);                    mw.visitVarInsn(ALOAD, 3);                    mw.visitVarInsn(ALOAD, 4);                    mw.visitVarInsn(ILOAD, 5);                    mw.visitMethodInsn(INVOKEVIRTUAL, classNameType,                                       "writeUnsorted", "(L" + JSONSerializer                                                        + ";Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/reflect/Type;I)V");                    mw.visitInsn(RETURN);                    mw.visitLabel(_else);                }            }            // isWriteDoubleQuoteDirect            if (context.writeDirect && !nonContext) {                Label _direct = new Label();                Label _directElse = new Label();                mw.visitVarInsn(ALOAD, 0);                mw.visitVarInsn(ALOAD, Context.serializer);                mw.visitMethodInsn(INVOKEVIRTUAL, JavaBeanSerializer, "writeDirect", "(L" + JSONSerializer + ";)Z");                mw.visitJumpInsn(IFNE, _directElse);                mw.visitVarInsn(ALOAD, 0);                mw.visitVarInsn(ALOAD, 1);                mw.visitVarInsn(ALOAD, 2);                mw.visitVarInsn(ALOAD, 3);                mw.visitVarInsn(ALOAD, 4);                mw.visitVarInsn(ILOAD, 5);                mw.visitMethodInsn(INVOKEVIRTUAL, classNameType,                                   "writeNormal", "(L" + JSONSerializer                                                  + ";Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/reflect/Type;I)V");                mw.visitInsn(RETURN);                mw.visitLabel(_directElse);                mw.visitVarInsn(ALOAD, context.var("out"));                mw.visitLdcInsn(SerializerFeature.DisableCircularReferenceDetect.mask);                mw.visitMethodInsn(INVOKEVIRTUAL, SerializeWriter, "isEnabled", "(I)Z");                mw.visitJumpInsn(IFEQ, _direct);                mw.visitVarInsn(ALOAD, 0);                mw.visitVarInsn(ALOAD, 1);                mw.visitVarInsn(ALOAD, 2);                mw.visitVarInsn(ALOAD, 3);                mw.visitVarInsn(ALOAD, 4);                mw.visitVarInsn(ILOAD, 5);                mw.visitMethodInsn(INVOKEVIRTUAL, classNameType, "writeDirectNonContext",                                   "(L" + JSONSerializer + ";Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/reflect/Type;I)V");                mw.visitInsn(RETURN);                mw.visitLabel(_direct);            }            mw.visitVarInsn(ALOAD, Context.obj); // obj            mw.visitTypeInsn(CHECKCAST, type(clazz)); // serializer            mw.visitVarInsn(ASTORE, context.var("entity")); // obj            generateWriteMethod(clazz, mw, getters, context);            mw.visitInsn(RETURN);            mw.visitMaxs(7, context.variantIndex + 2);            mw.visitEnd();        }        if (!nativeSorted) {            // sortField support            Context context = new Context(getters, beanInfo, classNameType, false,                                          DisableCircularReferenceDetect);            mw = new MethodWriter(cw, ACC_PUBLIC, "writeUnsorted",                                  "(L" + JSONSerializer + ";Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/reflect/Type;I)V",                                  null, new String[] { "java/io/IOException" });            mw.visitVarInsn(ALOAD, Context.serializer);            mw.visitFieldInsn(GETFIELD, JSONSerializer, "out", SerializeWriter_desc);            mw.visitVarInsn(ASTORE, context.var("out"));            mw.visitVarInsn(ALOAD, Context.obj); // obj            mw.visitTypeInsn(CHECKCAST, type(clazz)); // serializer            mw.visitVarInsn(ASTORE, context.var("entity")); // obj            generateWriteMethod(clazz, mw, unsortedGetters, context);            mw.visitInsn(RETURN);            mw.visitMaxs(7, context.variantIndex + 2);            mw.visitEnd();        }        // 0 writeAsArray        // 1 writeAsArrayNormal        // 2 writeAsArrayNonContext        for (int i = 0; i < 3; ++i) {            String methodName;            boolean nonContext = DisableCircularReferenceDetect;            boolean writeDirect = false;            if (i == 0) {                methodName = "writeAsArray";                writeDirect = true;            } else if (i == 1) {                methodName = "writeAsArrayNormal";            } else {                writeDirect = true;                nonContext = true;                methodName = "writeAsArrayNonContext";            }            Context context = new Context(getters, beanInfo, classNameType, writeDirect,                                          nonContext);            mw = new MethodWriter(cw, ACC_PUBLIC, methodName,                                  "(L" + JSONSerializer + ";Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/reflect/Type;I)V",                                  null, new String[] { "java/io/IOException" });            mw.visitVarInsn(ALOAD, Context.serializer);            mw.visitFieldInsn(GETFIELD, JSONSerializer, "out", SerializeWriter_desc);            mw.visitVarInsn(ASTORE, context.var("out"));            mw.visitVarInsn(ALOAD, Context.obj); // obj            mw.visitTypeInsn(CHECKCAST, type(clazz)); // serializer            mw.visitVarInsn(ASTORE, context.var("entity")); // obj            generateWriteAsArray(clazz, mw, getters, context);            mw.visitInsn(RETURN);            mw.visitMaxs(7, context.variantIndex + 2);            mw.visitEnd();        }        byte[] code = cw.toByteArray();        Class
         exampleClass = classLoader.defineClassPublic(classNameFull, code, 0, code.length);        Constructor
         constructor = exampleClass.getConstructor(SerializeBeanInfo.class);        Object instance = constructor.newInstance(beanInfo);        return (JavaBeanSerializer) instance;    }
       
      

再回退到上一步，查找调用链路：

// 如果没有找到，就创建一个类    public ObjectSerializer getObjectWriter(Class
      clazz) {        return getObjectWriter(clazz, true);    }    // classLoader 多次加载    private ObjectSerializer getObjectWriter(Class
      clazz, boolean create) {        ObjectSerializer writer = serializers.get(clazz);        if (writer == null) {            try {                final ClassLoader classLoader = Thread.currentThread().getContextClassLoader();                for (Object o : ServiceLoader.load(AutowiredObjectSerializer.class, classLoader)) {                    if (!(o instanceof AutowiredObjectSerializer)) {                        continue;                    }                    AutowiredObjectSerializer autowired = (AutowiredObjectSerializer) o;                    for (Type forType : autowired.getAutowiredFor()) {                        put(forType, autowired);                    }                }            } catch (ClassCastException ex) {                // skip            }            writer = serializers.get(clazz);        }        if (writer == null) {            final ClassLoader classLoader = JSON.class.getClassLoader();            if (classLoader != Thread.currentThread().getContextClassLoader()) {                try {                    for (Object o : ServiceLoader.load(AutowiredObjectSerializer.class, classLoader)) {                        if (!(o instanceof AutowiredObjectSerializer)) {                            continue;                        }                        AutowiredObjectSerializer autowired = (AutowiredObjectSerializer) o;                        for (Type forType : autowired.getAutowiredFor()) {                            put(forType, autowired);                        }                    }                } catch (ClassCastException ex) {                    // skip                }                writer = serializers.get(clazz);            }        }                if (writer == null) {            if (Map.class.isAssignableFrom(clazz)) {                put(clazz, MapSerializer.instance);            } else if (List.class.isAssignableFrom(clazz)) {                put(clazz, ListSerializer.instance);            } else if (Collection.class.isAssignableFrom(clazz)) {                put(clazz, CollectionCodec.instance);            } else if (Date.class.isAssignableFrom(clazz)) {                put(clazz, DateCodec.instance);            } else if (JSONAware.class.isAssignableFrom(clazz)) {                put(clazz, JSONAwareSerializer.instance);            } else if (JSONSerializable.class.isAssignableFrom(clazz)) {                put(clazz, JSONSerializableSerializer.instance);            } else if (JSONStreamAware.class.isAssignableFrom(clazz)) {                put(clazz, MiscCodec.instance);            } else if (clazz.isEnum() || (clazz.getSuperclass() != null && clazz.getSuperclass().isEnum())) {                JSONType jsonType = clazz.getAnnotation(JSONType.class);                if (jsonType != null && jsonType.serializeEnumAsJavaBean()) {                    put(clazz, createJavaBeanSerializer(clazz));                } else {                    put(clazz, EnumSerializer.instance);                }            } else if (clazz.isArray()) {                Class
      componentType = clazz.getComponentType();                ObjectSerializer compObjectSerializer = getObjectWriter(componentType);                put(clazz, new ArraySerializer(componentType, compObjectSerializer));            } else if (Throwable.class.isAssignableFrom(clazz)) {                SerializeBeanInfo beanInfo = TypeUtils.buildBeanInfo(clazz, null, propertyNamingStrategy);                beanInfo.features |= SerializerFeature.WriteClassName.mask;                put(clazz, new JavaBeanSerializer(beanInfo));            } else if (TimeZone.class.isAssignableFrom(clazz) || Map.Entry.class.isAssignableFrom(clazz)) {                put(clazz, MiscCodec.instance);            } else if (Appendable.class.isAssignableFrom(clazz)) {                put(clazz, AppendableSerializer.instance);            } else if (Charset.class.isAssignableFrom(clazz)) {                put(clazz, ToStringSerializer.instance);            } else if (Enumeration.class.isAssignableFrom(clazz)) {                put(clazz, EnumerationSerializer.instance);            } else if (Calendar.class.isAssignableFrom(clazz) //                    || XMLGregorianCalendar.class.isAssignableFrom(clazz)) {                put(clazz, CalendarCodec.instance);            } else if (Clob.class.isAssignableFrom(clazz)) {                put(clazz, ClobSeriliazer.instance);            } else if (TypeUtils.isPath(clazz)) {                put(clazz, ToStringSerializer.instance);            } else if (Iterator.class.isAssignableFrom(clazz)) {                put(clazz, MiscCodec.instance);            } else {                String className = clazz.getName();                if (className.startsWith("java.awt.") //                    && AwtCodec.support(clazz) //                ) {                    // awt                    if (!awtError) {                        try {                            put(Class.forName("java.awt.Color"), AwtCodec.instance);                            put(Class.forName("java.awt.Font"), AwtCodec.instance);                            put(Class.forName("java.awt.Point"), AwtCodec.instance);                            put(Class.forName("java.awt.Rectangle"), AwtCodec.instance);                        } catch (Throwable e) {                            awtError = true;                            // skip                        }                    }                    return  AwtCodec.instance;                }                                // jdk8                if ((!jdk8Error) //                    && (className.startsWith("java.time.") //                        || className.startsWith("java.util.Optional") //                    )) {                    try {                        put(Class.forName("java.time.LocalDateTime"), Jdk8DateCodec.instance);                        put(Class.forName("java.time.LocalDate"), Jdk8DateCodec.instance);                        put(Class.forName("java.time.LocalTime"), Jdk8DateCodec.instance);                        put(Class.forName("java.time.ZonedDateTime"), Jdk8DateCodec.instance);                        put(Class.forName("java.time.OffsetDateTime"), Jdk8DateCodec.instance);                        put(Class.forName("java.time.OffsetTime"), Jdk8DateCodec.instance);                        put(Class.forName("java.time.ZoneOffset"), Jdk8DateCodec.instance);                        put(Class.forName("java.time.ZoneRegion"), Jdk8DateCodec.instance);                        put(Class.forName("java.time.Period"), Jdk8DateCodec.instance);                        put(Class.forName("java.time.Duration"), Jdk8DateCodec.instance);                        put(Class.forName("java.time.Instant"), Jdk8DateCodec.instance);                        put(Class.forName("java.util.Optional"), OptionalCodec.instance);                        put(Class.forName("java.util.OptionalDouble"), OptionalCodec.instance);                        put(Class.forName("java.util.OptionalInt"), OptionalCodec.instance);                        put(Class.forName("java.util.OptionalLong"), OptionalCodec.instance);                                                writer = serializers.get(clazz);                        if (writer != null) {                            return writer;                        }                    } catch (Throwable e) {                        // skip                        jdk8Error = true;                    }                }                                if ((!oracleJdbcError) //                    && className.startsWith("oracle.sql.")) {                    try {                        put(Class.forName("oracle.sql.DATE"), DateCodec.instance);                        put(Class.forName("oracle.sql.TIMESTAMP"), DateCodec.instance);                                                writer = serializers.get(clazz);                        if (writer != null) {                            return writer;                        }                    } catch (Throwable e) {                        // skip                        oracleJdbcError = true;                    }                }                                if ((!springfoxError) //                    && className.equals("springfox.documentation.spring.web.json.Json")) {                    try {                        put(Class.forName("springfox.documentation.spring.web.json.Json"), //                            SwaggerJsonSerializer.instance);                                                writer = serializers.get(clazz);                        if (writer != null) {                            return writer;                        }                    } catch (ClassNotFoundException e) {                        // skip                        springfoxError = true;                    }                }                if ((!guavaError) //                        && className.startsWith("com.google.common.collect.")) {                    try {                        put(Class.forName("com.google.common.collect.HashMultimap"), //                                GuavaCodec.instance);                        put(Class.forName("com.google.common.collect.LinkedListMultimap"), //                                GuavaCodec.instance);                        put(Class.forName("com.google.common.collect.ArrayListMultimap"), //                                GuavaCodec.instance);                        put(Class.forName("com.google.common.collect.TreeMultimap"), //                                GuavaCodec.instance);                        writer = serializers.get(clazz);                        if (writer != null) {                            return writer;                        }                    } catch (ClassNotFoundException e) {                        // skip                        guavaError = true;                    }                }                if (className.equals("net.sf.json.JSONNull")) {                    try {                        put(Class.forName("net.sf.json.JSONNull"), //                                MiscCodec.instance);                    } catch (ClassNotFoundException e) {                        // skip                    }                    writer = serializers.get(clazz);                    if (writer != null) {                        return writer;                    }                }                if (TypeUtils.isProxy(clazz)) {                    Class
      superClazz = clazz.getSuperclass();                    ObjectSerializer superWriter = getObjectWriter(superClazz);                    put(clazz, superWriter);                    return superWriter;                }                // asm创建类是在这里生效的                if (create) {                    put(clazz, createJavaBeanSerializer(clazz));                }            }            writer = serializers.get(clazz);        }        return writer;    }

往前追踪，发现入口：

// TypeUtils, 获取所有get方法。    public static List
      
        computeGetters(Class
        clazz, //                                                 JSONType jsonType, //                                                 Map
       
         aliasMap, //                                                 Map
        
          fieldCacheMap, //                                                 boolean sorted, //                                                 PropertyNamingStrategy propertyNamingStrategy //    ) {        Map
         
           fieldInfoMap = new LinkedHashMap
          
           ();        for (Method method : clazz.getMethods()) {            String methodName = method.getName();            int ordinal = 0, serialzeFeatures = 0, parserFeatures = 0;            String label = null;            if (Modifier.isStatic(method.getModifiers())) {                continue;            }            if (method.getReturnType().equals(Void.TYPE)) {                continue;            }            if (method.getParameterTypes().length != 0) {                continue;            }            if (method.getReturnType() == ClassLoader.class) {                continue;            }            if (method.getName().equals("getMetaClass")                && method.getReturnType().getName().equals("groovy.lang.MetaClass")) {                continue;            }            JSONField annotation = method.getAnnotation(JSONField.class);            if (annotation == null) {                annotation = getSuperMethodAnnotation(clazz, method);            }            if (annotation != null) {                if (!annotation.serialize()) {                    continue;                }                ordinal = annotation.ordinal();                serialzeFeatures = SerializerFeature.of(annotation.serialzeFeatures());                parserFeatures = Feature.of(annotation.parseFeatures());                if (annotation.name().length() != 0) {                    String propertyName = annotation.name();                    if (aliasMap != null) {                        propertyName = aliasMap.get(propertyName);                        if (propertyName == null) {                            continue;                        }                    }                    FieldInfo fieldInfo = new FieldInfo(propertyName, method, null, clazz, null, ordinal,                                                        serialzeFeatures, parserFeatures, annotation, null, label);                    fieldInfoMap.put(propertyName, fieldInfo);                    continue;                }                if (annotation.label().length() != 0) {                    label = annotation.label();                }            }            if (methodName.startsWith("get")) {                if (methodName.length() < 4) {                    continue;                }                if (methodName.equals("getClass")) {                    continue;                }                if (methodName.equals("getDeclaringClass") && clazz.isEnum()) {                    continue;                }                char c3 = methodName.charAt(3);                String propertyName;                if (Character.isUpperCase(c3) //                    || c3 > 512 // for unicode method name                ) {                   if (compatibleWithJavaBean) {                        propertyName = decapitalize(methodName.substring(3));                    } else {                        propertyName = Character.toLowerCase(methodName.charAt(3)) + methodName.substring(4);                    }                    propertyName = getPropertyNameByCompatibleFieldName(fieldCacheMap, methodName,  propertyName,3);                 } else if (c3 == '_') {                    propertyName = methodName.substring(4);                } else if (c3 == 'f') {                    propertyName = methodName.substring(3);                } else if (methodName.length() >= 5 && Character.isUpperCase(methodName.charAt(4))) {                    propertyName = decapitalize(methodName.substring(3));                } else {                    continue;                }                boolean ignore = isJSONTypeIgnore(clazz, propertyName);                if (ignore) {                    continue;                }                //假如bean的field很多的情况一下，轮询时将大大降低效率                Field field = ParserConfig.getFieldFromCache(propertyName, fieldCacheMap);                                if (field == null && propertyName.length() > 1) {                    char ch = propertyName.charAt(1);                    if (ch >= 'A' && ch <= 'Z') {                        String javaBeanCompatiblePropertyName = decapitalize(methodName.substring(3));                        field = ParserConfig.getFieldFromCache(javaBeanCompatiblePropertyName, fieldCacheMap);                    }                }                                JSONField fieldAnnotation = null;                if (field != null) {                    fieldAnnotation = field.getAnnotation(JSONField.class);                    if (fieldAnnotation != null) {                        if (!fieldAnnotation.serialize()) {                            continue;                        }                        ordinal = fieldAnnotation.ordinal();                        serialzeFeatures = SerializerFeature.of(fieldAnnotation.serialzeFeatures());                        parserFeatures = Feature.of(fieldAnnotation.parseFeatures());                        if (fieldAnnotation.name().length() != 0) {                            propertyName = fieldAnnotation.name();                            if (aliasMap != null) {                                propertyName = aliasMap.get(propertyName);                                if (propertyName == null) {                                    continue;                                }                            }                        }                        if (fieldAnnotation.label().length() != 0) {                            label = fieldAnnotation.label();                        }                    }                }                if (aliasMap != null) {                    propertyName = aliasMap.get(propertyName);                    if (propertyName == null) {                        continue;                    }                }                                if (propertyNamingStrategy != null) {                    propertyName = propertyNamingStrategy.translate(propertyName);                }                FieldInfo fieldInfo = new FieldInfo(propertyName, method, field, clazz, null, ordinal, serialzeFeatures, parserFeatures,                                                    annotation, fieldAnnotation, label);                fieldInfoMap.put(propertyName, fieldInfo);            }            if (methodName.startsWith("is")) {                if (methodName.length() < 3) {                    continue;                }                if (method.getReturnType() != Boolean.TYPE                        && method.getReturnType() != Boolean.class) {                    continue;                }                char c2 = methodName.charAt(2);                String propertyName;                if (Character.isUpperCase(c2)) {                    if (compatibleWithJavaBean) {                        propertyName = decapitalize(methodName.substring(2));                    } else {                        propertyName = Character.toLowerCase(methodName.charAt(2)) + methodName.substring(3);                    }                    propertyName = getPropertyNameByCompatibleFieldName(fieldCacheMap, methodName,  propertyName,2);                 } else if (c2 == '_') {                    propertyName = methodName.substring(3);                } else if (c2 == 'f') {                    propertyName = methodName.substring(2);                } else {                    continue;                }                Field field = ParserConfig.getFieldFromCache(propertyName,fieldCacheMap);                if (field == null) {                    field = ParserConfig.getFieldFromCache(methodName,fieldCacheMap);                 }                JSONField fieldAnnotation = null;                if (field != null) {                    fieldAnnotation = field.getAnnotation(JSONField.class);                    if (fieldAnnotation != null) {                        if (!fieldAnnotation.serialize()) {                            continue;                        }                        ordinal = fieldAnnotation.ordinal();                        serialzeFeatures = SerializerFeature.of(fieldAnnotation.serialzeFeatures());                        parserFeatures = Feature.of(fieldAnnotation.parseFeatures());                                                if (fieldAnnotation.name().length() != 0) {                            propertyName = fieldAnnotation.name();                            if (aliasMap != null) {                                propertyName = aliasMap.get(propertyName);                                if (propertyName == null) {                                    continue;                                }                            }                        }                        if (fieldAnnotation.label().length() != 0) {                            label = fieldAnnotation.label();                        }                    }                }                if (aliasMap != null) {                    propertyName = aliasMap.get(propertyName);                    if (propertyName == null) {                        continue;                    }                }                                if (propertyNamingStrategy != null) {                    propertyName = propertyNamingStrategy.translate(propertyName);                }                //优先选择get                if (fieldInfoMap.containsKey(propertyName)) {                    continue;                }                FieldInfo fieldInfo = new FieldInfo(propertyName, method, field, clazz, null, ordinal, serialzeFeatures, parserFeatures,                                                    annotation, fieldAnnotation, label);                fieldInfoMap.put(propertyName, fieldInfo);            }        }        for (Field field : clazz.getFields()) {            if (Modifier.isStatic(field.getModifiers())) {                continue;            }            JSONField fieldAnnotation = field.getAnnotation(JSONField.class);            int ordinal = 0, serialzeFeatures = 0, parserFeatures = 0;            String propertyName = field.getName();            String label = null;            if (fieldAnnotation != null) {                if (!fieldAnnotation.serialize()) {                    continue;                }                ordinal = fieldAnnotation.ordinal();                serialzeFeatures = SerializerFeature.of(fieldAnnotation.serialzeFeatures());                parserFeatures = Feature.of(fieldAnnotation.parseFeatures());                if (fieldAnnotation.name().length() != 0) {                    propertyName = fieldAnnotation.name();                }                if (fieldAnnotation.label().length() != 0) {                    label = fieldAnnotation.label();                }            }            if (aliasMap != null) {                propertyName = aliasMap.get(propertyName);                if (propertyName == null) {                    continue;                }            }                        if (propertyNamingStrategy != null) {                propertyName = propertyNamingStrategy.translate(propertyName);            }            if (!fieldInfoMap.containsKey(propertyName)) {                FieldInfo fieldInfo = new FieldInfo(propertyName, null, field, clazz, null, ordinal, serialzeFeatures, parserFeatures,                                                    null, fieldAnnotation, label);                fieldInfoMap.put(propertyName, fieldInfo);            }        }        List
           
             fieldInfoList = new ArrayList
            
             (); boolean containsAll = false; String[] orders = null; JSONType annotation = clazz.getAnnotation(JSONType.class); if (annotation != null) { orders = annotation.orders(); if (orders != null && orders.length == fieldInfoMap.size()) { containsAll = true; for (String item : orders) { if (!fieldInfoMap.containsKey(item)) { containsAll = false; break; } } } else { containsAll = false; } } if (containsAll) { for (String item : orders) { FieldInfo fieldInfo = fieldInfoMap.get(item); fieldInfoList.add(fieldInfo); } } else { for (FieldInfo fieldInfo : fieldInfoMap.values()) { fieldInfoList.add(fieldInfo); } if (sorted) { Collections.sort(fieldInfoList); } } return fieldInfoList; }// SerializeConfig, 创建java bean. public ObjectSerializer createJavaBeanSerializer(SerializeBeanInfo beanInfo) { JSONType jsonType = beanInfo.jsonType; if (jsonType != null) { Class
              serializerClass = jsonType.serializer(); if (serializerClass != Void.class) { try { Object seralizer = serializerClass.newInstance(); if (seralizer instanceof ObjectSerializer) { return (ObjectSerializer) seralizer; } } catch (Throwable e) { // skip } } if (jsonType.asm() == false) { asm = false; } } Class
              clazz = beanInfo.beanType; if (!Modifier.isPublic(beanInfo.beanType.getModifiers())) { return new JavaBeanSerializer(beanInfo); } boolean asm = this.asm; if (asm && asmFactory.classLoader.isExternalClass(clazz) || clazz == Serializable.class || clazz == Object.class) { asm = false; } if (asm && !ASMUtils.checkName(clazz.getSimpleName())) { asm = false; } if (asm) { for(FieldInfo fieldInfo : beanInfo.fields){ Field field = fieldInfo.field; if (field != null && !field.getType().equals(fieldInfo.fieldClass)) { asm = false; break; } Method method = fieldInfo.method; if (method != null && !method.getReturnType().equals(fieldInfo.fieldClass)) { asm = false; break; } JSONField annotation = fieldInfo.getAnnotation(); if (annotation == null) { continue; } if ((!ASMUtils.checkName(annotation.name())) // || annotation.format().length() != 0 || annotation.jsonDirect() || annotation.serializeUsing() != Void.class ) { asm = false; break; } } } if (asm) { try { ObjectSerializer asmSerializer = createASMSerializer(beanInfo); if (asmSerializer != null) { return asmSerializer; } } catch (ClassFormatError e) { // skip } catch (ClassCastException e) { // skip } catch (Throwable e) { throw new JSONException("create asm serializer error, class " + clazz, e); } } return new JavaBeanSerializer(beanInfo); }
            
           
          
         
        
       
      

使用asmClassLoader加载动态类：

// 创建asmSerializer, 最后调用classloader加载类    private final JavaBeanSerializer createASMSerializer(SerializeBeanInfo beanInfo) throws Exception {        JavaBeanSerializer serializer = asmFactory.createJavaBeanSerializer(beanInfo);                for (int i = 0; i < serializer.sortedGetters.length; ++i) {            FieldSerializer fieldDeser = serializer.sortedGetters[i];            Class
      fieldClass = fieldDeser.fieldInfo.fieldClass;            if (fieldClass.isEnum()) {                ObjectSerializer fieldSer = this.getObjectWriter(fieldClass);                if (!(fieldSer instanceof EnumSerializer)) {                    serializer.writeDirect = false;                }            }        }             return serializer;    }

　　最后的代码报错是：java.lang.IllegalStateException: It is illegal to call this method if the current request is not in asynchronous mode (i.e. isAsyncStarted() returns false)，由于是写在动态生成的代码文件中，比较难查，解决问题已足够，不再深究。

　　理解这里的原因后，再来看问题，就简单多了，排除掉不支持转换的类或者使用其他方式获取想要的参数。

　　思考：如果让自己来设计框架，也需要考虑得更多；在用别人的框架的时候，也以一个开发者的角度考虑问题，如果不想考虑，可以直接参考其源码，发现其中的蹊跷；另外，测试一定是必不可少的，你可以借助测试部门，也可以自行测试，但是一定要考虑全面；最后，在做一些公用方法的变动时，一定不要太大意，宁可相信自己不无知，也不要相信代码一定不会出错，有条件情况下，尽可以使用try catch将其包裹，这样，在出问题的时候，也能迅速定位。

　　题外话：错误一定是会犯的，但是不要关键时候犯。