proguard混淆后导致json解析出错

gistfile1.java

private void parseJson() {

    String json = "{\"school\":{\"classes\": [{\"name\":\"one\",\"count\":1},{\"name\":\"two\",\"count\":2}],\"headMaster\" : \"Einstein\"}}";

    ObjectMapper mapper = new ObjectMapper();

    try {
        ResponseModle response = mapper.readValue(json, ResponseModle.class);

        Log.e(this.getClass().getName(), "headMaster : " + response.getSchool().getHeadMaster());
        Log.e(this.getClass().getName(), "class name : "
                + response.getSchool().getClasses().get(0).getName());

    } catch (JsonParseException e) {
        e.printStackTrace();
    } catch (JsonMappingException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    
    // 混淆后抛错
    // java.util.LinkedHashMap cannot be cast to me.relex.jsonparse.modle.ClassModle
    //  
    // 需要在proguard中加入
    // -keepattributes Signature 
    //
}

gistfile2.java

public class ResponseModle {

    private SchoolModle school;

    public SchoolModle getSchool() {
        return school;
    }

    public void setSchool(SchoolModle school) {
        this.school = school;
    }
}

gistfile3.java

public class SchoolModle {

    private List<ClassModle> classes;

    private String headMaster;

    public List<ClassModle> getClasses() {
        return classes;
    }

    public void setClasses(List<ClassModle> classes) {
        this.classes = classes;
    }

    public String getHeadMaster() {
        return headMaster;
    }

    public void setHeadMaster(String headMaster) {
        this.headMaster = headMaster;
    }

}

gistfile4.java

public class ClassModle {

    private String name;

    private int count;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }

}