我有一对相互依赖的二进制文件要解析。我正在使用Preon库。
这些文件被命名为rec.table 和rec.offset。一个是到另一个的偏移索引（rec.offset 文件的行 32 位整数，表示到 rec.table 的字节偏移）。rec.offset 中的行数取决于 rec.table 中可用的数据之一（recordCount 字段）。我需要提供偏移条目列表的大小，并且我需要使用该列表来访问记录条目，如下面的@BoundList 情况所示。
我有以下设置：
package bytecodeparsing;
import org.codehaus.preon.annotation.BoundList;
import org.codehaus.preon.annotation.BoundNumber;
public class RecTable {
// Using this instead of 'outer' due to circular dependencies
@SuppressWarnings("unused") // Actually used in Preon expression below
private RecOffsets recOffsets;
@BoundNumber int version;
@BoundList(size="4") byte[] pad; // 4 byte pad to ignore.
@BoundNumber long recordCount;
// offset is in RecOffsets, which must then be an outer class of this, but that class needs to know how many entries there
// are, which is the recordCount value here. Circular dependencies?
@BoundList(offset="recOffsets.offsets[index]", size="recordCount") Rec[] recs;
public void setDependencies(RecOffsets recOffsets) {
this.recOffsets = recOffsets;
}
}
和：
package bytecodeparsing;
import org.codehaus.preon.annotation.BoundList;
import org.codehaus.preon.annotation.BoundNumber;
public class RecOffsets {
@SuppressWarnings("unused") // Actually used in Preon expression below
private RecTable recTable; // maybe use this instead of 'outer' due to circular dependencies?
@BoundList(size="RecTable.recordCount+1") long[] offsets;
public void setDependencies(RecTable recTable) {
this.recTable = recTable;
}
}
当我运行它时，我收到一个类似于“ Parsing variable record lengths in Preon ”一文中报告的错误：
org.codehaus.preon.CodecConstructionException: Failed to construct codec.
at org.codehaus.preon.codec.ArrayCodecFactory.getSizeExpression(ArrayCodecFactory.java:152)
at org.codehaus.preon.codec.ArrayCodecFactory.create(ArrayCodecFactory.java:93)
at org.codehaus.preon.codec.CompoundCodecFactory.create(CompoundCodecFactory.java:59)
at org.codehaus.preon.DefaultCodecFactory$DecoratingCodecFactory.create(DefaultCodecFactory.java:266)
at org.codehaus.preon.codec.ObjectCodecFactory.harvestBindings(ObjectCodecFactory.java:184)
at org.codehaus.preon.codec.ObjectCodecFactory.createCodec(ObjectCodecFactory.java:129)
at org.codehaus.preon.codec.ObjectCodecFactory.create(ObjectCodecFactory.java:112)
at org.codehaus.preon.codec.CachingCodecFactory.create(CachingCodecFactory.java:130)
at org.codehaus.preon.codec.CompoundCodecFactory.create(CompoundCodecFactory.java:59)
at org.codehaus.preon.DefaultCodecFactory$DecoratingCodecFactory.create(DefaultCodecFactory.java:266)
at org.codehaus.preon.DefaultCodecFactory.create(DefaultCodecFactory.java:137)
at org.codehaus.preon.DefaultCodecFactory.create(DefaultCodecFactory.java:65)
at org.codehaus.preon.DefaultCodecFactory.create(DefaultCodecFactory.java:60)
at org.codehaus.preon.Codecs.create(Codecs.java:279)
at bytecodeparsing.PreonParsing.create(PreonParsing.java:76)
at bytecodeparsing.PreonParsing.<init>(PreonParsing.java:51)
Caused by: org.codehaus.preon.el.BindingException: Failed to create binding for bound data called recTable
at org.codehaus.preon.codec.BindingsContext.selectAttribute(BindingsContext.java:101)
at org.codehaus.preon.el.ImplicitsContext.selectAttribute(ImplicitsContext.java:52)
at org.codehaus.preon.el.LimboWalker.vexpr(LimboWalker.java:667)
at org.codehaus.preon.el.LimboWalker.vexpr(LimboWalker.java:488)
at org.codehaus.preon.el.Expressions.arithmetic(Expressions.java:125)
at org.codehaus.preon.el.Expressions.createInteger(Expressions.java:102)
at org.codehaus.preon.codec.ArrayCodecFactory.getSizeExpression(ArrayCodecFactory.java:148)
... 19 more
这个错误是指在偏移数组的大小属性中使用了recTable。与另一个问题一样，我可以通过提供一个常量大小或伪造一个简单的 @BoundNumber 绑定并引用它来克服这个错误。
在我上面链接的另一个问题中，用户遇到循环依赖跨两个类的情况，但是在解析一个文件时，我必须解析两个单独的文件。我假设 Wilfred Springer 提到的补丁（PREON-9）已经集成到 github 存储库（在 PREON-48）。
我该如何处理这种循环依赖？我错过了一个技巧吗？